p8T 


111 


HE  PREPARATION  OF 

SUBSTANCES 


CHARLES  A.  PETERS 


B    3    12D    DES 


Agric.  uept 


'*i?y^ 


The  Preparation  of  Substances 
Important  in  Agriculture 

A  Laboratory  Manual  of  Synthetic 
Agricultural  Chemistry 


THIRD  EDITION 
BY 


CHARLES   A.    PETERS,   Ph.Di 

Professor  of  Inorganic  and  Soil  Chemistry 

Department  of  General  and  Agricultural  Chemistry 

Massachusetts  Agricultural  College 


i  >^   \.^\'\\  '' 


NEW  YORK 

JOHN  WILEY  &  SONS,  Inc. 

London:    CHAPMAN  &    HALL,   Limited 

1919 


\ 

I.  \ 


( 


AGRIC. 
LIBRARY 


Uh. 


Copyright,  1919, 

BY 

C.  A.   PETERS 


•    •    ♦ 


Stanbopc  iprcss 

F.    H.GILSON   COMPANT 
BOSTON,  U.S.A. 


PREFACE 


It  has  been  the  aim  in  this  manual  to 
select  substances  of  agricultural  interest, 
adapt  them  to  laboratory  preparation,  and 
explain  their  chemistry  to  the  best  of  our 
present  knowledge  not  overlooking  their 
practical  significance. 

The  work  was  at  first  nothing  more  than 
laboratory  directions,  but  the  interest  of  the 
student  gradually  required  the  addition  of 
explanatory  matter  to  such  a  degree  that 
the  emphasis  on  an  accompanying  text  has 
been  greatly  reduced.  The  method  of  pres- 
entation aims  to  put  a  few  major  points 
before  the  student  and  extend  the  work  on 
such  points  over  so  long  a  time  that  the 
student  will  absorb  it.  The  author  feels 
that  when  a  student,  in  his  earlier  years  in 
college,  works  interestedly  for  a  whole  exer- 
cise around  one  thing  he  grasps  something 
while  if  a  dozen  important  points  pass  in 
review  during  the  time  he  is  left  in  a  maze 
and  gets  little  but  technical  benefit.  While, 
however,   the  student   is   busy  on  the  one 

ill 

394027 


iv  Preface 

major  piece  of  work  other  minor  points  may 
be  gatherd  around  it  and  are  readily  ab- 
sorbd. 

In  this  collection  of  agricultural  material 
it  is  interesting  to  note  the  points  that  are 
brot  home  to  the  student  as  the  work 
develops  Among  these  are  oxidation,  neu- 
tralization, distillation,  crystallization,  sat- 
uration, chemical  calculations,  metathesis, 
mass  action,  double  salts,  equilibrium  and 
colloids.  By  making  a  process  necessary 
to  the  production  of  material  the  student 
must  grasp  it  or  fail  in  the  experiment. 
Take  the  seemingly  simple  matter  of  satura- 
tion. It  is  but  the  work  of  a  minute  to  ex- 
plain what  is  meant  by  the  process;  the 
student  will  give  an  intelligent  expression  of 
the  phenomenon  in  a  second  minute;  how- 
ever, when  in  the  laboratory  he  is  making  a 
preparation  from  two  others,  the  success  of 
which  depends  upon  the  preparation  of  two 
saturated  solutions,  then,  and  not  until  then, 
does  the  student  understand  saturation. 

Only  about  half  of  the  students  entering 
this  college  have  had  farm  experience.  It  is 
difficult  to  interest  a  student  in  the  prepara- 
tion of  superphosphate  or  Bordeaux  mixture 
unless  he  knows  something  of  its  use,  hence 
the  amount  of  space  given  in  the  notes  to  the 
practical  use  of  each  substance.     This  does 


Preface  V 

not  lessen  the  value  of  the  material  for 
chemical  instruction  but  rather  enhances 
it. 

The  work  was  designd  for  students  in  an 
agricultural  college  who  have  already  had 
such  a  knowledge  of  chemistry  as  is  acquired 
from  a  year's  work  in  the  high  school.  It  is 
intended  to  be  done  in  two  or  three  hour 
laboratory  periods,  and  furnishes  sufficient 
material  for  one  semester  of  such  exercises. 
The  arrangement  of  the  work  is  such  that  a 
laboratory  full  of  students  can  all  be  doing 
the  same  thing  at  the  same  time  without 
extended  waiting;  procedures,  such  as  crys- 
tallization and  cooling,  taking  place  in  the 
interim  between  exercises.  With  us  it  is 
customary  to  score  the  preparation  when 
completed,  as  one  would  butter  or  milk, 
allowing  something  for  quality  and  some- 
thing for  quantity  and  to  give  credit  for  the 
exercise  only  upon  completion  of  the  prepara- 
tion. 

The  author  is  endeted  to  Professor  A.  A. 
Blanchard  of  the  Massachusetts  Institute  of 
Technology  not  only  for  the  development  of 
synthetic  method  of  laboratory  work  for  first 
year  work  in  college,  but  also  for  the  privilege 
to  adapt  three  preparations  from  his  book, 
Synthetic  Inorganic  Chemistry,  for  use  in 
this   manual.     The   three   preparations    are 


vi  Preface 

Potassium  Nitrate,  Copper  Sulfate  and  Lead 
Nitrate. 

The  appreciation  of  the  author  is  also 
exprest  to  Dr.  H.  S.  Adams  of  New  Bruns- 
wick, N.  J.,  who  was  associated  with  this 
work  in  its  early  stages,  and  to  Professor 
Ernest  Anderson  of  this  laboratory  who  has 
given  this  course  for  several  years.  Valuable 
suggestions  have  come  from  both  these  men. 

The  first  edition  was  printed  privately  in 
1914;  the  second  was  again  mimeographed 
in  1916;  the  third  is  herewith  offerd  to  those 
laboratories  that  have  used  the  manual  since 
1914  and  to  others  that  wish  to  experience 
the  fascination  of  the  synthetic  method  in 
agricultural  chemistry. 

A  few  simplified  spelhngs  have  been  used. 

Amherst,  Mass., 
August  1,  1918. 


CONTENTS 

Page 

Superphosphate 1 

Sulfate  of  Ammonia 13 

Potassium  Nitrate 20 

Potash  Salts 26 

Sulfate  of  Potash-Magnesia 26 

Sulfate  of  Potash  (High  Grade) 28 

Muriate  of  Potash 30 

Lead  Nitrate 38 

Lead  Arsenate 41 

Lime-Sulfur 50 

Copper  Sulfate 69 

Paris  Green 64 

Bordeaux  Mixture 68 

Emulsions 78 


Vll 


1  >      >      >    J        » 


The  Preparation  of  Substances 
Important  in  Agriculture 

SUPERPHOSPHATE 

Superphosphate  is  made  from  the  natural 
rock  phosphate,  finely  ground,  and  sulfuric 
acid,  the  phosphate  being  acted  upon  as 
shown  in  equation  (1)  which  follows: 

(1)   CagPsOs  +  2H2SO4  •  aq  =  CaH4Po08  •  H2O 
+  2CaS04  •  2H2O.  ^^^"^ 

Calcium  sulfate  (gypsum)  ,       ,    ^ 

phosphate 

Two-thirds  of  the  calcium  of  the  tricalcium 
phosphate  are  replaced  by  the  hydrogen  of  the 
acid.  Chamber  sulfuric  acid  is  used.  It  is 
necessary  to  calculate  the  actual  amount  of 
tricalcium  phosphate  in  the  material  at  hand, 
the  amount  of  sulfuric  acid  to  act  on  200 
grams  of  this  material  and  the  amount  of 
water  that  must  be  added  to  the  sulfuric  acid 
to  make  it  of  the  proper  strength. 

Calculations.  —  (a)  Note    the    purity    of 

the  phosphate  rock  and  calculate  the  number 

of  grams  (a)  of  the  tricalcium  phosphate  in 

1 


2  ;^  • :  ,\  .'Preparation, of  Substances 

200  grams  of  the  material  used.     Record  the 
amount. 

(6)  From  the  equation  given  above  cal- 
culate the  number  of  grams  (b)  of  H2SO4 
necessary  to  react  with  (a)  grams  of  Ca3P208. 
Note  the  number. 

(c)  Read  the  specific  gravity  of  the 
chamber  acid  from  the  spindle  floating  in  the 
acid  on  the  side  shelf,  Refer  to  the  table  of 
specific  gravity  and  read  off  the  weight  of 
the  H2SO4  in  1  cc.  of  the  chamber  acid. 
Calculate  the  number  of  cubic  centimeters 
of  chamber  acid  (c)  necessary  to  contain 
the  (6)  grams  of  H2SO4.  Record  the 
volum. 

(d)  The  chamber  acid  is  too  strong  to  be 
used  directly  on  the  rock  phosphate  and  must 
be  diluted  until  it  has  the  specific  gravity 
1.53.  Calculate  the  number  of  cubic  centi- 
meters {d)  of  this  acid  necessary  to  contain 
(b)  grams  of  sulfuric  acid.  This  is  the  volum 
to  which  (c)  cubic  centimeters  of  chamber 
acid  should  be  diluted  before  the  rock  phos- 
phate is  added  to  it.     Record  the  number. 

Tabulate  the  results  of  the  four  calcula- 
tions as  indicated  below  and  have  them  veri- 
fied by  an  instructor  before  proceding  with 
the  work. 


Superphosphate  3 

(a)  Weight   of  Ca3P208  in  200   grams    rock   phos- 

phate,   grams. 

(b)  Weight  of  H2SO4  required  for  200  grams  rock 

phosphate, grams. 

(c)  Volum  of  chamber  acid  required  for  200  grams 

rock  phosphate, cc. 

(d)  Volum  to  which  the  (c)  cc.  of  chamber  acid  must 

be  diluted, cc. 

-  Procedure.  —  Measure  out  the  volum  (c) 
of  chamber  acid  and  pour  it  into  (d-c)  cubic 
centimeters  of  water  in  a  porcelain  dish. 
Weigh  out  200  grams  of  the  rock  phosphate 
and  stir  it  slowly  into  the  acid.  Let  the 
mixture  stay  in  the  evaporating  dish  until 
the  next  exercise.  The  hydrofluoric  acid 
fumes  that  arise  are  to  be  avoided. 

Notebook;   Test  for  Soluble  Phosphates. 

—  Shake  a  little  of  the  superphosphate  with 
water,  filter  the  solution,  add  to  the  filtrate  a 
solution  of  ammonium  molybdate  and  warm 
the  liquid  gently  in  a  test  tub^.  If  the  yellow 
precipitate  of  ammonium  phosphomolybdate 
does  not  form  after  a  few  seconds  its  ap- 
pearance may  be  hast  end  by  adding  a  gram 
or  two  of  solid  ammonium  nitrate.  The 
addition  of  ammonium  hydroxid  followd 
by  nitric  acid  will  accomplish  the  same  result 
including  the  heating;  when  this  is  done  the 
solution  must  be  left  acidic  with  nitric  acid. 

If  some  of  the  natural  rock  phosphate  is 


4  Preparation  of  Substances 

treated  similarly  it  will  be  seen  that  only  an 
inappreciable  amount  of  phosphate  dissolvs 
in  water. 

Test  for  Lime.  —  Dissolv  some  of  the 
superphosphate  in  water  and  filter  as  before. 
To  the  clear  filtrate  add  a  solution  of  oxalic 
acid  or  ammonium  oxalate.  The  white 
precipitate  that  forms  is  calcium  oxalate 
which  shows  the  presence  of  calcium  com- 
pounds in  solution. 

NOTES 

The  Beaum^  hydrometer  is  an  instrument 
for  determining  density  that  has  wide  indus- 
trial use.     It  is,  however,  unscientific  as  it  has 


Sulfuric  Acid. 


Specific  Gravity  of  Aqueous  Solu- 
tions 


De^irees  B6. 

Sp.  gr. 

1  cc.  contains  grams 
H2SO4. 

50.0 

1.53 

0.957 

50.6 

1.54 

0.977 

51.2 

1.55 

0.996 

52.8 

1.56 

1.015 

52.4 

1.57 

1.035 

53  0 

1.58 

1.054 

53.6 

1.59 

1.075 

54.1 

1.60 

1.096 

54.7 

1.61 

1.118 

55.2 

1.62 

1.139 

two  separate  scales,  one  for  liquids  heavier 
than  water  and  rre  for  liquids  lighter  than 
water,  the  two  having  no  relation.     Further, 


Superphosphate  5 

neither  scale  bears  any  relation  to  true  specific 
gravity.  See  Thorp,  Inorganic  Chemical 
Preparations,  p.  32. 

The  solubility  of  the  natural  rock  phosphate, 
or  floats,  in  a  short  time  under  most  soil 
conditions,  is  so  sUght  that  it  has  become  a 
common  practise  to  ''dissolv"  it,  that  is, 
to  convert  it  into  the  water-soluble  acid 
phosphate  having  only  one-third  of  the  ori- 
ginal amount  of  calcium.  Under  ordinary 
business  conditions  one-half  of  all  the  sul- 
furic acid  made  in  this  country  is  used  in  this 
process. 

Tricalcium  phosphate,  whether  as  rock 
phosphate,  bones  or  the  mineral  apatite,  is 
always  associated  with  fluorin  and  generally 
chlorin.  In  addition  rock  phosphate  is  gen- 
erally associated  with  calcium  and  magnesium 
carbonates,  and  sometimes  iron  and  alumi- 
num phosphates  so  that  the  reactions  which 
take  place  with  the  sulfuric  acid  are  more 
complicated  than  that  given  at  the  beginning 
of  this  exercise.  The  following  are  the  more 
important : 

(2)  2Ca3P208  •  Ca2FP04  +  7H2SO4  •  aq  = 

3CaH4P208  •  H2O  +  7CaS04  •  2H2O 
+  2HF. 

(3)  CaCOs  +  H2SO4  .  aq  =  CaS04  •  2H2O 

+  CO2. 

(4)  2AIPO4  +  3H2SO  .aq  =  2H3PO.  + 

2A1(S04)3  •  I8H2O. 


6  Preparation  of  Substances 

The  fertilizer  manufacturer  must  determin 
the  exact  amount  of  sulfuric  acid  to  be  used 
for  each  substance  present  in  the  ground  rock. 
The  student  is  not  askt  to  do  this.  How- 
ever, to  insure  the  presence  of  sufficient  acid 
to  combine  with  all  these  substances,  the 
calcium  phosphate  content  of  the  floats  as 
given  to  the  student  is  increased  5  to  10  per 
cent. 

The  strength  of  sulfuric  acid  used  will  vary 
according  to  the  source  and  composition  of 
the  natural  rock.  If  large  amounts  of  cal- 
cium compounds  other  than  phosphate  are 
present  a  more  dilute  acid  is  used  so  that 
there  will  be  water  enuf  to  hj^drate  the 
land  plaster  (calcium  sulfate)  formd  in  the 
reaction. 

The  calcium  fluorid  present  reacts  with 
the  sulfuric  acid  producing  the  disagreeable 
poisonous  hydrofluoric  acid  gas.  Avoid 
breathing  the  fumes  from  the  mixture. 

Notice  that  after  standing  the  mass  crum- 
bles easily  in  the  hand.  After  storing  several 
weeks,  during  which  time  the  action  of  the 
sulfuric  acid  continues  until  the  insoluble 
phosphates  are  reduced  to  a  fraction  of  one 
per  cent,  the  material  is  ground,  if  necessary, 
and  put  on  the  market  or  used  as  a  ''base," 
i.e.,  one  of  the  substances  from  which  fer- 
tilizers are  made. 


L^ 


Superphosphate  7 

There  being  several  calcium  compounds  in 
the  rock  phosphate  which  all  appear  finally 
as  hydrated  calcium  sulfate  (gypsum)  it  is 
not  strange  that  the  resulting  superphos- 
phate is  composed  of  60-70  per  cent  of 
gypsum.  From  this  it  is  easy  to  see  why 
superphosphate  contains  only  14  to  16  per 
cent  of  phosphoric  acid  (P2O5). 

The  deposits  of  rock  phosphate  at  present 
being  extensivly  workt  are  found  in  South 
Carolina,  Florida  and  Tennessee.  The  larg- 
est and  most  newly  discoverd  deposits  are 
in  Idaho,  Utah  and  Wyoming. 

A  good  grade  of  ground  rock  carries  65  per 
cent  of  tricalcium  phosphate  and  the  material 
not  infrequently  runs  over  80  per  cent.  In- 
ferior rock  containing  a  few  per  cent  of 
phosphoric  acid  and  mixt  with  carbonate 
of  lime  is  abundant,  but  it  is  not  economical 
to  ship  this  any  great  distance  or  treat  it 
with  sulfuric  acid. 

The  use  of  '^  raw  rock  "  vs.  ^'dissolvd  rock  " 
is  a  much  discust  question  in  agriculture. 
Thru  the  East,  on  fight  soils  and  for  intensiv 
cultivation,  the  dissolvd  rock  is  used  ex- 
clusivly;  for  some  of  the  heavy  soils  of  the 
West  raw  rock  is  recommended  in  connection 
with  decaying  organic  matter.  According  to 
Professor  Hopkins  of  Illinois  the  raw  rock  in 
a  heavy  soil  is  converted  to  dissolvd  rock 


8  Preparation  of  Substances 

by  acid  in  the  soil,  the  steps  in  the  process 
being  first,  the  production  of  ammonium 
carbonate,  (NH4)2C03,  from  the  amino 
groups,  —  NH2,  in  the  plant;  second,  the 
oxidation  of  ammonia  to  nitrous  acid  by 
bacteria;  third,  the  conversion  of  the  raw 
rock  to  dissolvd  rock  by  the  action  of  the 
nitrous  acid  which  may  be  represented  by 
the  equation, 

Ca3P208  +  4HNO2  +  H2O  =  CaH4P208  •  H2O 

+  2Ca(N02)2; 

and  fourth,  the  oxidation  of  the  calcium 
nitrite,  Ca(N02)2,  to  calcium  nitrate, 
Ca(N03)2,  by  the  action  of  bacteria.  Both 
the  acid  phosphate  and  the  calcium  nitrate 
resulting  from  the  action  are  available  to  the 
plants  for  food.  Naturally  the  plants  richest 
in  amino  groups,  such  as  clovers  and  alfalfa, 
are  most  desirable  to  plow  under  with  the 
raw  rock.  This  action  of  the  dissolving  of 
raw  rock  by  acid  in  the  soil  has  been  demon- 
strated by  Professor  Hopkins  in  the  labora- 
tory, but  others  deny  that  it  actually  takes 
place  in  the  soil. 

As  a  general  conclusion  it  may  be  said 
that  all  the  phosphorus  of  acid  phosphate 
is  immediately  available  to  plants  while  only 
a  small  amount  of  the  phosphorus  in  the 
raw  rock  is  available  during  one  growing 


Superphosphate  9 

season;  however,  the  phosphorus  in  raw  rock 
continues  to  become  available,  year  by  year, 
until  the  total  amount  is  drawn  upon.  For 
cultural  purposes  the  important  question  is 
whether  or  not  there  is  sufficient  phosphorus 
available  in  one  season  for  the  crop  in  ques- 
tion; this,  of  course,  depends  upon  many 
factors  which  cannot  be  gone  into  here. 
.  Analysis  of  Rock  Phosphate.  —  An  analy- 
sis of  Tennessee  rock  phosphate  taken  from 
the  American  Fertilizer  Handbook  for  1908 
is  here  given: 

Per  cent 

Moisture  (loss  on  drying) 0.87 

Combined  water  and  organic  matter 

(loss  on  ignition) 1 .  53 

Sand  and  insoluble  matter 2.76 

Ferric  oxid,  Fe203 2.40 

Almnina,  AI2O3 1 .  99 

Lime,  CaO 49.07 

Magnesia,  MgO 0.24 

Carbon  dioxid,  CO2 1 .  08 

Fluorin,  F 2.98 

Sulfur  trioxid,  SO3 1.03 

Phosphoric  acid,  P2O5 35 .  62 

99.57 

When  these  figures  are  put  together  in  an 
attempt  to  show  the  substances  that  existed 
in  the  original  rock  the  data  shown  under 
colum  (a)  is  obtaind.  The  composition  of 
another  sample  of  rock  phosphate  is  shown 


10 


Preparation  of  Substances 


in  colum   (6).     It  is  noticeable  that   many 
of  the  constituents  vary  widely  in  quantity. 


Moisture  and  organic  matter 

Phosphate  of  lime,  Ca3P20s 

Phosphates  of  iron  and  aluminium 

FeP04,  AIPO4 

Carbonate  of  lime,  CaCOa 

Carbonate  of  magnesia,  MgCOa  . . . 

Fluorid  of  lime,  CaF2 

Iron  pyrites,  FeS2 

Iron  oxid,  Fe203 

Alumina,  AI2O 

Sand  and  silicious  matter 


(a) 

Per  cent 

2.30 

77.76 

4^43 

0.50 

6.11 

0.77 

1.88 

1.99 

2.76 

98.50 

(&) 


Per  cent 

1.00 
55.00 

6.50 
3.50 
0.75 
2.25 


28.00 
100.00 


The  natural  soiu"ces  of  phosphorus  are 
the  mineral  apatite,  or  phosphorite,  which  is 
an  ingredient  of  nearly  all  soils.  It  has  the 
same  formula  as  the  raw  rock  phosphate  but 
is  entirely  different  in  appearance.  Immense 
deposits  of  this  mineral  are  localized  in 
Quebec  and  Ontario,  Canada. 


QUESTIONS 
(To  be  answerd  in  the  notebook.) 

1.  What  is  the  per  cent  of  P2O5  in  calcium  dihy- 
drogen  phosphate? 

2.  Supposing  equation  (2)  to  represent  all  that 
happens  when  sulfuric  acid  acts  upon  rock  phosphate, 
calculate  the  per  cent  of  hydrated  acid  phosphate  and 

^he    per    cent    of    hydrated    calcium    sulfate   in   the 
mixture. 


Superphosphate  11 

3.  Again  supposing  equation  (2)  to  represent  what 
happens  when  superphosphate  is  made,  what  is  the 
highest  per  cent  of  P2OS  it  is  possible  to  have  in  super- 
phosphates? 

4.  What  per  cant  of  P2O5  is  present  in  ordinary 
superphosphata?  Name  the  substance  represented  by 
the  symbol  P2O5. 

5.  What  per  cent  of  tricalcium  phosphate  is  found 
in  natural  phosphates? 

6.  Which  would  use  the  more  sulfuric  acid,  a  raw 
rock  carrying  60  per  cent  tricalcium  phosphate  and 
5  per  cent  calcium  carbonate  or  a  rock  carrying  55  per 
cent  tricalcium  phosphate  and  10  per  cent  calcium 
carbonate? 

7.  What  gases  escape  during  the  action  of  the  sul- 
furic acid  on  the  rock  phosphate?  Which  is  poison- 
ous? 

8.  What  compounds  are  found  in  the  raw  rock? 
In  the  dissolvd  rock?  The  student  cannot  give,  for 
example,  calcium  oxide,  CaO,  or  phosphorus  pentoxid, 
P2O5,  as  compounds  present  in  either  the  raw  or  dis- 
solvd rock  altho  such  compounds  are  well  known  and 
moreover  are  represented  in  the  table  of  analysis.  In 
the  raw  and  dissolvd  rocks  the  lime  and  the  phosphoric 
acid  are  in  combination  and  the  student  should  give, 
as  well  as  he  can,  the  actual  lime  and  phosphorus  com- 
pounds that  are  present. 

9.  How  could  phosphoric  acid  be  made  by  a  process 
similar  to  that  for  making  superphosphate? 

10.  How  could  the  acid  phosphate  be  made  into  a 
neutral  salt?     How  would  the  solubility  change? 

11.  Write  a  symbol  for  another  acid  calcium  phos- 
phate; name  the  compound. 

12.  How  is  the  test  made  for  soluble  phosphate? 

13.  Describe  the  test  for  lime. 


12  Preparation  of  Substances 

14.  How  many  grams  of  actual  sulfuric  acid  in  a 
liter  of  dilute  acid  of  a  density  of  51.5  Be.? 

15.  Where  are  the  phosphate  deposits  in  this 
country? 

16.  Where  should  a  plant  for  making  superphosphate 
be  located?  Near  the  phosphate  mines  or  near  the 
farmer?     Give  reasons  for  the  answer. 

17.  ^^^lat  is  meant  by  the  terms,  "  raw  rock,"  "  dis- 
solvd  rock  "  ? 

18.  Where  is  the  use  of  dissolvd  rock  recommended? 

19.  Is  calcium  sulfate  soluble  in  water?  (See  text 
under  calcium  compounds.) 

20.  Write  symbols  for  limestone;  slaked  lime;  quick- 
lime. 


SULFATE   OF  AMMONIA 

Sulfate  of  ammonia  is  made  by  distilling 
the  ammonia  from  the  gas  liquor  into  sulfuric 
acid.  The  first  problem  is  to  find  out,  ap- 
proximately, how  much  gas  liquor  should  be 
used  to  neutralize  a  convenient  amount,  say 
15  cc,  of  chamber  sulfuric  acid. 

Calculations.  —  Read  the  specific  gravity 
spindle  floating  in  the  sulfuric  acid  and  cal- 
culate, from  the  table  on  page  4,  the  amount 
of  actual  sulfuric  acid  in  the  15  cc.  to  be  used. 
From  the  equation, 

2NH3  +  H2SO4    =    (NH4)2S04, 

find  out  how  many  grams  of  ammonia  are 
necessary  to  unite  with  this  amount  of  acid. 

Ascertain  the  strength  of  the  gas  liquor 
and  compute  the  volum  necessary  to  con- 
tain the  desired  amount  of  ammonia. 

For  example:  If  30  grams  of  ammonia 
(NII3)  are  desired  and  the  gas  liquor  is  8  per 

cent  ammonia,  there  will  be  — -—  =  125  grams 

0.08 

required.     The  density  of  gas  liquor  being 

nearly  the  same  as  water,  125  cc.  in  place 

of  125  grams  may  be  considerd  the  correct 

amount. 

13 


14  Preparation  of  Substances 

Enter  the  results  as  given  below  and  have 
them  verified  by  an  instructor. 

Amount  of  actual  acid  in  15  cc.  of  chamber  acid, .  .grams. 

Amount  of  ammonia  equivalent  to  the  acid, grams. 

Volum  of  gas  hquor  to  contain  the  ammonia, cc. 

Procedure  —  Arrange  a  distilling  appa- 
ratus consisting  of  a  flask  of  a  capacity  of 
from  500  to  1000  cc.  carrying  a  two-hole  rub- 
ber stopper.  Thru  one  hole  put  a  thistle 
tube  reaching  to  within  1  cm.  of  the  bottom 
of  the  flask,  thru  the  other  hole  insert  a 
bent  tube  carrying  a  one-hole  stopper  fitted 
to  a  condenser.  Put  15  cc.  of  chamber  sul- 
furic acid  into  a  250-cc.  gas  bottle  and  adjust 
to  the  delivery  tube  of  the  condenser  so  that 
the  bottle  rests  on  the  desk  and  the  delivery 
tube  dips  under  the  acid.  Draw  from  10 
to  50  cc.  more  than  the  calculated  amount 
of  gas  liquor,  —  the  amount  depending 
on  its  strength,  —  pour  it  thru  the  thistle 
tube  into  the  flask  and  begin  heating.  As 
soon  as  the  distillation  is  well  under  way, 
look  for  the  deposit  of  ammonium  carbonate 
in  the  condenser.  If  any  appears  —  as  it 
always  does  —  it  will  be  necessary  to  break 
up  this  compound  in  the  flask  by  adding  lime. 
To  do  this  make  a  paste  of  10  to  15  grams  of 
lime  and  50  to  75  cc.  of  water  and  pour 
the  mixture,  which  is  milk  of  lime,  thru  a 


Sulfate  of  Ammonia  15 

piece  of  cheese  cloth  placed  over  the  thistle 
tube.  The  reaction  results  in  the  precipi- 
tation of  calcium  carbonate  in  the  flask, 

Ca02H2  +  (NH4)2C03  =  CaCOa  +  2NH3 
+  2H2O, 

and  the  liberation  of  ammonia  which  vola- 
tilizes faster  than  the  ammonium  carbonate. 

When  the  sulfuric  acid  is  entirely  neutra- 
lized, as  is  shown  by  the  action  of  litmus 
paper  or  a  decided  change  in  the  appearance 
of  the  distillate,  disconnect  the  apparatus. 
Filter  the  solution  of  ammonium  sulfate  in 
the  gas  bottle  if  tariy  matter  has  collected  in 
it,  first  making  sure  that  all  the  ammonium 
sulfate  is  in  solution,  and  evaporate  the  clear 
filtrate  in  a  porcelain  dish  to  the  point  of 
crysta'lization. 

Cool  the  mixture,  bring  the  mass  of  crystals 
on  a  paper  filter  and  allow  them  to  drain  and 
further  dry  by  pressing  between  filter  papers. 
Weigh  the  crystals  and  enter  the  amount  in 
the  notebook. 

To  become  familiar  with  the  properties  of 
the  salt,  heat  a  little  in  a  dry  test  tube  and 
hold  a  piece  of  moistend  red  litmus  in  the 
mouth  of  the  tube.  Ammonium  sulfate 
melts  at  140°;  at  280°  it  decomposes,  losing 
ammonia  and  leaving  behind  ammonium 
acid  sulfate. 


16  Preparation  of  Substances 

NOTES 

The  time  of  the  student  is  such  an  impor- 
tant factor  that  considerable  more  than  the 
required  amount  of  ammonia  is  recommended 
for  use.  This  obviates  waiting  for  all  the 
ammonia  to  be  driven  off  and  also  saves 
evaporation  of  the  increased  amount  of  water 
which  would  distil  over.  Of  com^se  a  waste 
of  ammonia  results.  Industrially  such  a 
waste  of  ammonia  would  not  be  allowd. 

If  the  evaporation  procedes  beyond  a  cer- 
tain point  the  mass  upon  cooling  will  be  solid 
salt.  In  this  case  filtering  and  drying  are 
unnecessary.  The  danger  in  using  this 
quicker  method  of  drying  lies  in  the  fact  that 
the  solution  of  ammonium  sulfate  in  water 
upon  being  heated  to  dryness  passes  over  into 
a  clear  molten  anhydrous  mass  so  quickly  that 
the  change  may  not  be  noticed.  Heating  this 
molten  anhydrous  mass  results  in  the  decom- 
position of  the  salt  as  explaind  in  a  previous 
paragraf. 

In  the  manufacture  of  coal  gas,  by  heating 
soft  coal  much  of  the  nitrogen  present  is 
combined  with  hydrogen  forming  ammonia. 
Some  of  the  oxygen  that  enters  the  retorts  as 
they  are  charged  combines  with  the  carbon 
forming  carbon  dioxid.  This  weak  acid, 
carbonic   acid,   unites  with   the  weak  base 


Sulfate  of  Ammonia  17 

ammonia  and  forms  the  volatil  salt,  am- 
monium carbonate.  Part  of  the  process  of 
pm-ification  of  coal  gas  consists  in  washing 
out  the  ammonia  and  ammonium  carbonate 
in  water.  This  wash  is  known  as  dilute  gas 
liquor  (2|  oz.  of  ammonia  to  the  gallon) 
and  may  be  concentrated  by  distillation. 
Such  a  concentrated  product  contains  the 
equivalent  of  about  18  oz.  of  ammonia 
(NH3)  per  gallon  of  liquid. 

The  United  States  normally  produces 
about  300,000  tons  of  sulfate  of  ammonia 
annually.  Since  the  war  the  production  has 
doubled  and  is  constantly  increasing.  It  is  a 
plant  food  furnishing  both  nitrogen  and  sulfur; 
excessive  use  as  a  fertilizer,  however,  may 
deplete  the  soil  of  its  calcium. 

The  milk  of  lime  which  decomposes  the 
ammonium  carbonate  must  be  straind  or 
the  lumps  will  clog  the  thistle  tube.  In 
place  of  the  procedure  described  the  mixture 
may  be  allowd  to  settle  four  or  five  seconds 
after  stirring  and  the  upper  portion  pourd 
thru  the  thistle  tube  leaving  the  lumps  be- 
hind on  the  bottom  of  the  container. 

Should  the  process  of  distillation  be  inter- 
rupted before  the  sulfuric  acid  is  neutral- 
ized the  product  will  be  a  mixture  of  the 
neutral  and  acid  ammonium  sulfates. 

Sometimes  the  tarry  materials  exist  in  the 


18  Preparation  of  Substances 

neutralized  solution  in  colloidal  condition 
and  are  not  flocculated  until  the  ammonium 
sulfate  solution  has  become  more  concen- 
trated. Should  flocculation  occur  during  the 
course  of  evaporation  the  tarry  substance 
then  may  be  filterd  out.  It  is  this  material 
left  in  the  preparation  which  gives  the  pecu- 
liar brownish  color  to  commercial  sulfate  of 
ammonia. 

The  point  of  crystallization  is  determind 
by  blowing  across  the  surface  of  the  hot 
liquid.  When  a  scima  appears  at  once  the 
evaporation  by  flame  may  cease. 

QUESTIONS 
(To  be  answerd  in  the  notebook.) 

1.  How  many  grams  of  amimonia  in  2  kilos  of  a  solu- 
tion containing  28.33%? 

2.  How  much  ammonia  in  250  cc.  of  a  solution  of  a 
sp.  gr.  of  0.970  containing  7.31%  of  NH3? 

3.  How  many  tons  of  ammonium  sulfate  could  be 
made  from  a  tank  car  of  concentrated  ammonia  con- 
taining 5000  gallons  of  14%  NH3?  The  weight  of  a 
gallon  may  be  taken  as  8  pounds.  What  is  this  worth 
at  $60.00  per  ton? 

4.  What  is  the  per  cent  of  ammonia  in  ammonium 
sulfate? 

5.  Write  the  reactions,  giving]  the  names,  showing 
how  two  different  salts  may  be  made  by  putting  to- 
gether ammonium  hydroxid  and  sulfuric  acid. 

6.  What  other  substances  in  addition  to  ammonia 
are  produced  by  distilling  soft  coal? 


Sulfate  of  Ammonia  19 

7.  What  is  the  use  of  the  Ume  in  the  distillatioD  of 
gas  hquor? 

8.  Explain  the  presence  of  ammonium  carbonate  in 
gas  hquor. 

9.  Why  is  commercial  sulfate  of  ammonia  brown? 
10.   Why  does  a  brown  substance  sometimes  settle 

out  during  the  concentration  of  the  ammonium  sul- 
fate solution? 


POTASSIUM   NITRATE 

Potassium  nitrate  is  made  by  metathesis  of 
potassium  chlorid  and  sodium  nitrate,  taking 
advantage  of  the  different  solubiUties  of  the 
four  possible  salts  in  hot  and  cold  water. 

Procedure.  —  Heat  200  cc.  of  water  in  a 
porcelain  dish  and  when  hot  add  100  grams 
of  sodium  nitrate  and  90  grams  of  muriate 
of  potash.  Evaporate  until  the  volum  is 
reduced  to  about  100  cc,  and  filter  off  the 
sodium  chlorid,  sand  and  dirt  thru  a 
carefully  prepared  Witt  filter.  Throw  away 
the  residue  on  the  filter,  and  cool  the  fil- 
trate until  the  crystals  of  potassium  nitrate 
appear  in  quantity. 

Some  care  is  required  to  judge  when  the  solution  is 
boild  down  to  one-haH  its  original  volum.  If  it  is 
filterd  too  soon,  in  which  case  few  or  no  potassium 
nitrate  crystals  separate  out  of  the  filtrate  on  cooling, 
the  filtrate  should  be  evaporated  further  and  again 
filterd  to  remove  the  sodium  chlorid  which  will  sepa- 
rate as  solution  boils  away.  If  the  mixture  boils  too 
long  before  filtering  the  crystallization  of  the  potas- 
sium nitrate  will  take  place  in  the  funnel  stem  and 
clog  the  filter.  In  such  a  case  the  whole  mass  should  be 
put  back  in  the  dish  with  about  50  cc.  more  of  water 
and  reheated.     It  sometimes  aids  the  filtermg  to  warm 

20 


Potassium  Nitrate  21 

the  funnel  just  previous  to  using.  This  can  be  done 
by  pouring  a  test  tube  of  hot  water  thru,  the  funnel. 
Empty  out  the  water. 

Filter  off  the  crystals  of  potassium  nitrate 
when  the  solution  is  cold;  set  the  crystals 
aside.  Evaporate  the  filtrate  again  until 
reduced  about  one-half  its  volum,  or  until 
crystals  of  sodium  chlorid  appear  in  quan- 
tity, filter  thru  the  Witt  plate,  rejecting 
the  sodium  chlorid  on  the  filter  and  cool  the 
filtrate  to  the  lowest  point  possible  to  crystal- 
lize the  potassium  nitrate.  Filter  off  this 
crop  of  potassium  nitrate,  and  put  with 
the  quantity  previously  obtaind.  As  both 
crops  of  crystals  came  from  a  solution 
saturated  with  sodium  chlorid  as  well  as 
potassium  nitrate  and  as  sodium  chlorid  is 
slightly  less  soluble  (4  grams  per  100  cc.)  in 
cold  water  than  hot  some  sodium  chlorid 
crystals  will  have  formd  on  the  nitrate.  To 
get  rid  of  these,  dissolv  the  nitrate  in  hot 
water,  using  about  50  cc.  or  less  for  every 
100  grams  of  crystals,  and  cool  in  cold  water 
as  was  done  before.  Filter.  The  mother 
liquor  should  contain  all  the  sodium  chlorid 
and  if  the  mother  liquor  adhering  to  the 
crystals  on  the  filter  can  be  replaced  by  water 
before  they  dry  out  the  product  will  be  free 
from  chlorid.  Wash  the  crystals  with  cold 
water,  a  drop  at  a  time,  until  a  few  of  the 


22  Preparation  of  Substances 

crystals  in  water  in  a  test  tube  give  no  test 
for  chlorin  ions  when  a  soluble  silver  salt  is 
added. 

The  microscope  can  be  used  to  advantage  here. 
If  square  right  angle  blocks  (sodium  chlorid)  are 
formd  adhering  to  the  long  nitrate  bars  the  crystals 
will  have  to  be  redissolvd.  If  no  blocks  of  sodium 
chlorid  are  seen  it  may  be  taken  for  granted  that 
purification  may  be  brot  about  by  continued,  drop  by 
drop,  washing  wdth  cold  water.  The  crystals  when 
pure  may  be  dried  by  pressing  between  filter  paper  or 
by  allowing  to  stand  over  one  exercise. 

NOTES 

The  Witt  filter  consists  of  a  perforated 
porcelain  disk  in  a  funnel  fitted  into  a 
heavy  glass  suction  flask,  having  connection 
with  an  aspirator.  It  is  a  convenient 
and  rapid  means  of  filtering  when  prop- 
erly used.  The  student  should  be  supplied 
with  paper  filters  of  a  diameter  about  one 
centimeter  greater  than  that  of  the  porcelain 
plate.  Should  the  plates  become  chipt  they 
can  still  be  used  if  a  small  piece  of  filter 
paper  is  torn  off  and  laid  over  the  damaged 
place.  Unless  the  chipt  place  is  so  closed 
pressure  will  make  a  hole  in  the  filter  paper 
allowing  the  precipitate  to  pass  thru  into  the 
filtrate. 

The  flask  should  be  supphed  with  rubber 
tubing  of  ordinary  thickness,   not  pressure 


Potassium  Nitrate  23 

tubing,  and  a  pinchcock  to  help  regulate  the 
pressure.  The  proper  use  consists  in  ar- 
ranging the  apparatus,  starting  the  pump, 
emptying  the  mixture  on  the  filter,  closing 
the  rubber  tube  with  the  pinchcock  and 
then  shutting  off  the  water.  As  the  vacuum 
in  the  flask  is  relieved  it  can  be  increased  by 
starting  the  pump  and  momentarily  opening 
the  pinchcock.  Too  much  use  of  the  pump 
is  to  be  avoided. 

It  is  only  in  exceptional  cases  where  potas- 
sium nitrate  is  of  agricultural  importance. 
True,  it  contains  both  potash  and  nitrogen  in 
one  compound  and  therefore  in  concentrated 
form,  but  these  substances  are  as  well  sup- 
plied in  agriculture  by  the  sodium  nitrate  and 
the  potassium  chlorid  separately.  In  isolated 
localities  where  the  freight  rate  is  exception- 
ally high  it  is  possible  that  the  cost  of  manu- 
facture of  potassium  nitrate  would  be  less 
than  the  freight  on  the  sodium  chlorid  elimi- 
nated in  the  process.  In  such  a  locality  it 
might  be  desirable  to  use  potassium  nitrate 
for  fertilizer. 

The  classic  use  of  potassium  nitrate  is  for 
black  powder.  Sodium  nitrate  being  hygro- 
scopic does  not  make  a  powder  suitable  for 
use  in  fire  arms;  however  a  coarse  blasting 
powder  is  made  from  it,  the  large  grains 
being  glazed  to  keep  out  moisture. 


24  Preparation  of  Substances 

When  the  two  salts  are  dissolve!  in  water 
all  four  ions,  K+,  Na+,  CI",  NOs",  exist  as 
well  as  all  possible  combinations  of  these. 
As  water  evaporates  the  least  soluble  com- 
bination of  ions,  sodium  chlorid,  w^ill  come  out 
of  solution  tirst,  so  that  the  reaction  procedes 
by  metathesis, 

KCl  +  NaNOs  =  KNO3  +  NaCl. 

It  is  to  be  noted  in  this  reaction  that  as  the 
Na  and  CI  ions  form  the  least  soluble  sub- 
stance so  do  the  two  ions  remaining  after 
these  unite,  K+  and  NOs",  form  the  most 
soluble  combination.  Either  circumstance 
would  be  sufficient  to  determin  the  direc- 
tion of  the  reaction. 

The  change  in  solubility  of  the  potassium 
nitrate  in  hot  and  cold  solution  is  very  great. 
When  hot  potassium  nitrate  is  many  times 
more  soluble  than  sodium  chlorid;  at  33°, 
their  molar  solubilities  are  equal  and  below 
that  temperature  potassium  nitrate  is  less 
soluble,  being  about  one-half  that  of  sodium 
chlorid  at  10°. 

A  graphic  representation  of  the  solubilities 
of  these  salts  will  be  of  aid  to  the  student. 
Such  figures  are  found  in  the  following  texts: 
Kahlenberg,  p.  435;  Alexander  Smith,  p.  131; 
Blanchard,  Synthetic  Inorganic  Chemistry, 
p.  26. 


Potassium  Nitrate  25 

QUESTIONS 
(To  be  answerd  in  the  notebook.) 

1.  How  many  grams  of  potassimn  chlorid  are 
required  to  miite  with  100  grams  of  sodium  nitrate? 
Keep  one  decimal  place  in  the  figure. 

2.  Of  what  use  is  potassium  nitrate? 

3.  Write  the  symbols  of  the  four  salts  that  exist 
in  solution  at  the  begiiming  of  this  experiment.  Write 
symbols  for  the  ions. 

4.  W^hat  is  the  solubility  of  potassium  nitrate  at 
100°?  of  sodium  chlorid? 

5.  What  is  the  solubility  of  these  two  salts  at  room 
temperature  or  the  temperature  of  hydrant  water? 
State  the  exact  temperature  selected. 

6.  Describe  a  test  for  chlorid  ions. 

7.  Describe  the  crystals  of  potassium  nitrate;  of 
sodium  chlorid. 

8.  When  might  it  be  desirable  to  use  potassium 
nitrate  as  a  fertilizer? 

9.  Where  is  sodium  nitrate  found?  What  is  its 
common  name?  Why  is  it  not  used  for  making  gun 
powder? 

10.  If  one  kilo  of  a  solution  of  salt  saturated  at  100^ 
is  coold  to  10°  how  many  grams  of  salt  will  separate 
out?  Consult  the  rrafs  in  one  of  the  references  given 
in  the  last  paragraf  before  the  question. 


POTASH   SALTS 

PART   I 
SULFATE   OF  POTASH-MAGNESIA 

The  sulfate  of  potash-magnesia  is  made 
according  to  the  equation, 

3KC1  +  2MgS04  •  H2O  +  IIH2O  =  K2SO4  . 
MgS04  •  6H2O  +  KCl .  MgCl2  •  6H2O, 

by  mixing  saturated  brines  of  potassium 
chlorid  and  magnesium  sulfate. 

Procedure.  —  Weigh  out  60  grams  of 
muriate  of  potash  and  add  it,  as  fast  as  it  will 
dissolv,  to  about  100  cc.  of  boiling  water. 
Makmg  sure  that  all  the  salt  is  in  solution 
filter  the  mixture  while  hot  through  a  Witt 
plate  to  separate  the  iron  oxid,  dirt  and  sand. 
Put  the  filtrate  in  a  beaker,  keep  the  liquid 
at  boiling  temperature,  and  concentrate  the 
brine  until  crystals  of  potassium  chlorid  begin 
to  appea,r  on  the  surface,  showing  that  the 
solution  is  saturated  at  that  temperature. 

While  the  foregoing  is  in  operation  weigh 
out  100  grams  of  kieserit  and  dissolv  it  in 
about  75  cc.  of  boiling  water,  adding  the 
salt  slowly.  In  case  it  does  not  all  go  into 
solution,  indicated  by  a  residue  of  salt  on  the 

26 


Sulfate  of  Potash- Magnesia  27 

bottom  of  the  beaker  and  a  scum  on  the 
surface  of  the  Kquid,  add  10  or  20  cc.  more 
of  water  and  heat,  repeating  the  addition  of 
small  amounts  of  water  and  heating,  if 
necessary,  until  the  magnesium  sulfate  is 
all  dissolvd.  Filter,  using  the  Witt  plate, 
and  concentrate  the  clear  filtrate  until  the 
liquid  is  saturated  as  indicated  by  the  for- 
mation of  a  scum  on  the  surface.  Mix 
the  two  hot  saturated  salt  solutions  and  set 
the  mixture  aside  for  at  least  twelve  hours. 
Both  the  solutions  must  be  saturated  upon 
mixing  or  the  experiment  will  be  a  failure. 
The  crystals  that  begin  to  form  upon  put- 
ting the  solutions  together  and  which  further 
separate  on  cooling  are  the  double  sulfates  of 
potassium  and  magnesium,  K2SO4  •  MgS04- 
6H2O,  sometimes  cald  the  sulfate  of  potash- 
magnesia. 

After  the  mixture  has  stood,  filter  off  the 
crystals,  drain  them  well  on  a  Witt  plate, 
transfer  them  to  a  paper  and  weigh.  Save 
the  filtrate  which  contains  a  solution  of  arti- 
ficial carnallit. 

The  crystals  of  double  sulfate  may  be  dried 
in  a  few  hours  by  spreading  on  paper  when 
the  exact  weight  may  be  obtaind  or  the 
approximate  weight  may  be  had  at  once, 
assuming  that  5  to  6  per  cent  of  the  weight  is 
water  adhering  to  the  crystals. 


PART  II 
SULFATE   OF   POTASH,    HIGH-GRADE 

It  is  customary  to  make  sulfate  of  potash 
from  the  double  salt  by  adding  sufficient 
potassium  chlorid  to  carry  on  the  following 
reaction : 

3KC1  +  K2SO4  •  MgS04  •  6H2O  =  2K2SO4  + 
KCl  .  MgCl2  .  6H2O. 

Procedure.  —  Calculate  the  amount  of 
potassium  chlorid  necessary  to  react  with 
the  am.ount  of  double  salt  at  hand,  and  weigh 
out  enuf  muriate  of  potash  to  furnish  this 
amount  of  actual  salt,  allowing  for  impurity. 
Heat  the  necessary  amount  of  water  to  boil- 
ing, dissolv  the  salt,  filter  off  the  dirt  on  a  Witt 
plate,  and  heat  the  filtrate  until  it  is  satu- 
rated all  as  previously  described  under  sul- 
fate of  potash-magnesia. 

Add  the  sulfate  of  potash-magnesia  to 
boiling  water,  using  100  cc.  for  every  80  grams 
of  salt,  and  put  this  mixture  with  the  hot 
saturated  solution  of  the  chlorid.  Potas- 
sium sulfate  begins  to  separate  at  once  and 
continues  to  come  out  on  cooling.  After 
standing  24  hours  the  salt  may  be  filterd  off 

28 


Sulfate  of  Potash,  High-Grade         29 

and  dried  in  the  air.     Record  the  weight  of 
driei  salt. 

Tne  filtrate,  which  should  be  saved,  also 
contains  the  double  chlorids  of  potassium  and 
magnesium  (carnallit)  similar  to  that  obtaind 
under  Part  I. 


PART  III 
MURIATE   OF  POTASH 

Procedure.  —  Put  the  two  filtrates  contain- 
ing the  artificial  carnalUt  brine  together  and 
evaporate  the  water  until  the  hollow  octahe- 
dral crystals  of  potassium  chlorid  appear  in 
abundance.  The  decomposition  of  the  car- 
nalht  yields  some  potassium  chlorid  which 
crystalhzes  out  first;  this  is  rapidly  followd 
by  the  clear  dense  crystals  of  the  carnallit 
itself.  The  latter  may  compose  the  major 
portion  of  the  precipitate.  If  too  much  or 
nearly  all  the  water  is  evaporated  off  mag- 
nesium chlorid  will  separate  out  making  the 
product  dehquescent.  The  crystals  may  be 
separated  from  the  magnesium  chlorid  brine 
by  the  use  of  the  Witt  plate.  The  filtrate 
containing  the  solution  of  magnesium  chlorid 
may  be  thrown  away. 

The  two  salts,  sulfate  of  potash  and  muri- 
ate of  potash,  dried  and  weighd,  are  handed 
in  separately. 

NOTES 

The  amount  of  water  used  to  dissolv 
the  salts  may  be  quite  a  little  more  than 
would    be    calculated    from    the    solubility 

30 


Muriate  of  Potash  31 

tables.  There  are  several  reasons  for  this. 
First,  there  are  impurities  present  which  if 
they  contain  an  ion  in  common  with  the 
principal  salt  may  necessitate  the  use  of  more 
water.  To  illustrate  this  suppose  there  are 
10  grams  of  sodium  chlorid  in  every  50  grams 
of  the  crude  potassium  chlorid  (a  chlorid  ion 
in  common),  then  it  is  necessary  to  furnish 
water  for  the  sodium  chlorid  as  well  as  for 
the  potassium  chlorid;  while  if  10  grams  of 
calcium  nitrate  were  present  (no  common  ion : 
K+,  Ca+,  NO.s",  C1-)  this  substance  would 
dissolv  in  the  solution  already  saturated  with 
potassium  chlorid.  Second,  sufficient  water 
should  be  present  so  that  the  solutions  may 
be  filterd  before  they  approach  saturation; 
otherwise  the  crystallization  that  results  on 
cooling  clogs  the  filter  and  causes  delay. 

In  filtering  all  such  mixtures  which  con- 
tain fine  sediment,  first  allow  them  to  settle 
and  bring  the  solid  matter  onto  the  filter 
only  at  the  end  of  the  operation  after  the 
clear  liquid  has  past  thru  the  filter. 

Kieserit,  the  magnesium  sulfate  with  one 
molecule  of  water,  is  the  salt  that  has  sepa- 
rated out  in  the  German  deposits.  Ordinarily 
from  water  the  heptahydrate,  MgS04  •  7H2O, 
separates  out.  Epsom  salts,  the  hepta- 
hydrate, are  made  from  kieserit  by  dissolving 
kieserit  and  allowing  the  salt  to  crystallize. 


32  Preparation  of  Substances 

In  all  this  work  it  is  the  object  to  precipi- 
tate a  salt  by  mixing  two  hot  saturated  solu- 
tions. The  appearance  of  ciystais  or  a  scum 
(film  of  fine  crystals)  on  the  surface  may  be 
taken  as  an  indication  of  saturation.  Mixing 
solutions  which  are  not  saturated  may  result 
in  large  loss  of  the  desired  substance.  Often 
the  addition  or  withdrawal  of  one  cubic 
centimeter  of  water  is  all  that  is  necessary 
to  produce  the  condition  sought. 

In  dissolving  the  double  sulfate  in  water  the 
salt  may  not  appear  to  dissolv  completely. 
This  is  immaterial  as  the  residue  is  potassium 
sulfate,  the  same  as  the  desired  product.  It 
is  possible  to  crystallize  out  potassium  sul- 
fate by  evaporating  the  solution  of  potash- 
magnesia  sulfate. 

Muriate  of  pota^sh  is  sold  in  three  grades 
containing  80,  95  and  98  per  cent,  respec- 
tively. The  material  containing  80  per  cent 
potassium  chlorid  is  the  grade  mostly  used 
for  fertilizers.  This  is  produced  industrially 
by  treating  the  raw  salts  as  they  are  mined 
with  a  hot  saturated  solution  of  magnesium 
chlorid  such  as  is  thrown  away  at  the  end 
of  this  experiment.  The  resulting  hot  solu- 
tion is  coold  in  cement  tanks  and  the  crude 
muriate  of  potash  separates  out.  The  crys- 
tals are  centrifuged  and  further  dried  over  a 
fire  in  sloping  pans  about  10  x  60  feet  in 


Muriate  of  Potash  33 

size.  Bromin  is  obtaind  from  the  magne- 
sium bromid  in  the  spent  magnesium  chlorid 
brine. 

In  former  3^ears  one  of  the  salts  mined 
extensively  in  Germany  was  carnallit  in  a  high 
degree  of  purity.  Such  deposits  are  no  longer 
available,  and  in  its  place  the  carnallit  brine 
appears  from  which  the  high  grade,  96  to  98 
per  cent,  muriate  of  potash  is  made  by  con- 
centration and  crystallization. 

The  American  sources  of  potash  which 
have  been  investigated  since  1908  and  devel- 
oped since  the  war  are  the  giant  kelps  of  the 
Pacific  coast,  the  nativ  potash-bearing  rocks, 
the  products  of  blast  furnaces  and  cement 
kilns  and  the  salts  of  inland  lakes.  A  brief 
discussion  of  each  source  is  given. 

The  kelps  exert  a  selective  action  on  the 
salts  in  the  sea  and  take  up  relatively  more 
potassium  chlorid  than  other  compounds. 
When  the  kelp  is  dried  and  incinerated  the 
ash  contains  15  to  50  per  cent  muriate  of 
potash.  The  cost  of  production  is  so  high, 
however,  that  the  procedure  is  not  economi- 
cal. On  the  other  hand  an  ingenious  fer- 
mentation process  has  been  devised,  pro- 
ducing acetone  and  esters  as  the  principal 
products  and  potash  as  a  by-product.  This 
is  in  successful  operation  on  the  Pacific  coast. 

The  amount  of  potash  in  such  minerals  as 


34  Preparation  of  i:substances 

feldspar  is  unlimited,  but  here  again  the 
cost  of  production  is  so  great  that  little 
potash  is,  as  yet,  produced  from  this  source. 
Another  mineral  containing  large  quantities 
of  potash  is  found  in  Utah  and  called  alunite. 
This  substance  contains  silicates  and  sul- 
fates of  potassium  and  aluminium  which  on 
heating  furnish  water  soluble  sulfate  of  pot- 
ash. Six  hundred  tons  a  month  of  potas- 
sium sulfate  were  being  produced  in  1918 
from  this  source. 

Potash  is  being  produced  in  this  country, 
England  and  France  from  the  blast  furnaces 
of  the  steel  industry.  The  limestone,  iron  ore, 
and  coke  used  in  the  smelting  may  each  con- 
tain some  potash;  if  so  during  the  heating 
some  of  this  is  volatilized.  Special  devices, 
electrical  precipitators,  take  the  potash-bear- 
ing dust  out  of  the  gases  as  they  pass  from  the 
furnaces.  Potassium  chlorid  is  the  substance 
obtaind.  As  there  is  generally  insufficient 
chlorin  to  combine  with  the  potassium  the 
amount  of  substance  volatilized  is  limited  by 
the  chlorin  available.  The  addition  of  com- 
mon salt,  sodium  chlorid,  to  the  furnace 
charge  consequently  increases  the  amount 
of  potash  recoverd.  It  is  said  that  there  is 
sufficient  potash  available  from  this  source  to 
furnish  the  entire  needs  of  this  country. 

The  cement  kilns  also  volatilize  potassium 


Muriate  of  Potash  35 

chlorid  from  potash  compounds  present  in 
the  hmestone  and  sihcates  used  in  their 
manufacture.  The  material  is  very  fine  and 
would  be  lost  as  ''  smoke  "  if  the  particles 
were  not  charged  ^\dth  electricity  and  then 
caused  to  deposit  on  strong  electrically 
charged  plates  in  the  Cottrell  process  of 
electrical  precipitation. 

Searles  Lake  in  the  California  desert  con- 
tains over  12  square  miles  of  a  crystal  de- 
posit 70  feet  thick.  These  crystals  are 
surrounded  by  a  saturated  brine  carrying 
about  5  per  cent  of  potassium  chlorid.  The 
brine  contains  two  bases,  sodium  and  potas- 
sium; and  four  acids,  chlorides,  sulfates, 
borates  and  carbonates.  Potassium  chlorid 
and  borax  are  the  products  of  this  industry. 
It  is  calculated  that  there  are  30  million 
tons  of  potash  in  this  region  which  in  itself 
is  sufficient  to  supply  the  needs  of  America 
for  25  or  more  years. 

The  work  outlined  in  this  exercise  deals 
with  double  salts  occasiond  by  the  presence 
of  magnesium  when  the  magnesium  is  absent, 
as  in  most  of  the  American  deposits,  the 
process  of  crystalUzation  is  much  simphfied. 

The  size  of  the  crystal  generally  varies 
with  the  rapidity  with  which  it  forms.  If 
the  salt  forms  quickly,  the  crystals  are  small; 
if  more  slowly,  the  crystals  are  larger. 


36  Preparation  of  Substances 

'  Each  of  the  crystals  has  its  definit  shape  which  is 
easily  seen  under  the  microscope.  Reference  is  given 
to  various  figures  of  crystals  in  Watt's  Dictionary  of 
Chemistry,  Vol.  II,  pages  148  ff. 

The  hydrated  double  sulfate  of  potassium  and  mag- 
nesium is  inclined  to  form  coarse  monoclinic  prisms 
which  lo.k  hke  half  cubes  or  diamonds  which  have 
been  prest  so  that  the  upper  faces  are  not  directly  over 
the  lower  ones.     Compare  Figs.  285  and  287. 

Potassium  chlorid,  hke  sodium  chlorid,  appears  in 
cubes  or  colums,  or  commonly  as  a  four-sided  funnel 
or  hollow  pjTamid. 

Potassimn  sulfate  may  be  in  small  hexagonal  prisms 
(really  rhombic)  or  in  longer  prisms  with  a  bluntly 
tapering  end.  Vid.  Figs.  272  and  297.  Similar  figures 
are  shown  in  Gmelin-Kraut,  Vol.  2i,  p.  49. 

Magnesium  sulfate  is  inclined  to  grow  in  long 
needles  (rhombic)  with  faces  on  the  very  abrupt  end. 
Vid.  Fig.  281. 

Magnesium  chlorid,  MgCl2  •  6H2O,  forms  mono- 
clinic  prisms  much  like  the  double  sulfate  of  potash- 
magnesia.    Vid.  Figs.  285  and  287. 

QUESTIONS 
(To  be  answerd  in  notebook.)] 

1.  Calculate  the  per  cent  of  potash,  K2O,  in  the 
sulfate  of  potash-magnesia;  in  potassium  sulfate;  in 
potassium  chlorid.     Express  results  as  follows: 

K2O         94.3   ^  ^^^^^^^ 


K2SO4      174.4 

2.  Tell  when  a  solution  is  saturated. 

3.  How  many  pounds  of  potassium  chlorid  in  a  ton 
of  muriate  of  80  per  cent  grade? 


Muriate  of  Potash  37 

4.  How  much  potash  is  there  in  a  ton  of  kainit 
containing  12  per  cent  KoO? 

'5.  If  potassium  chlorid  and  magnesium  sulfate 
solutions  are  mixt  what  salt  is  most  likely  to  be  pre- 
cipitated?   Why? 

6.  What  is  the  solubility  of  four  salts  used  in  the 
exercise?  Express  relatively  at  some  definite  tem- 
perature, putting  the  most  soluble  at  the  head  of  the 
colum. 

7.  What  materials,  in  addition  to  sodium  chlorid,  go 
to  make  up  the  20%  impurities  in  ordinary  muriate 
of  potash? 

8.  How  does  the  double  sulfate  of  potash-magnesia 
decompose  upon  being  dissolvd  in  a  small  quantity 
of  water? 

9.  What  use  is  made  industrially  of  the  magnesium 
chlorid  brine  that,  in  this  exercise,  is  thrown  away  after 
the  high-grade  muriate  of  potash  has  b3en  filterd  off? 

10.  Deicribs  the  American  sources  of  potash. 


LEAD   NITRATE 

Lead  nitrate  is  made  from  litharge,  PbO, 
and  nitric  acid. 

Calculation.  —  From  the  equation, 

PbO  +  2HNO3  =  Pb(N03).2  +  H2O, 

calculate  the  amount  of  nitric  acid  required 
to  act  on  20  grams  of  lead  oxid.  Read  the 
spindle  floating  in  the  nitric  acid  to  be  used 
and,  by  reference  to  the  table  at  the  end  of 
this  exercise,  ascertain  how  many  grams  of 
actual  nitric  acid  in  one  cubic  centimeter  of 
this  liquid.  By  division  find  out  how  many 
cubic  centimeters  of  this  nitric  acid  must 
be  used. 

Enter  the  results  in  the  following  form: 

Nitric  acid  required,  grams, 

Density  of  nitric  acid  solution, 

Number  grams  nitric  acid  in  1  cc, 

Volume  of  nitric  acid  solution,  required,  cc, 

Procedure.  —  Weigh  out  20  grams  of 
litharge,  and  place  it  in  a  small  beaker  with 
the  required  amount  of  nitric  acid.  Heat 
until  the  oxid  is  converted  to  nitrate  and 
solution  results,  adding  more  water,  if  neces- 
sary, to  dissolv  the  crystals  of  lead  nitrate. 

38 


Lead  Nitrate  39 

If  a  white  precipitate  of  lead  sulfate  is  pres- 
ent the  mixture  must  be  filterd  to  remove  the 
lead  sulfate.  Heat  the  filtrate,  or  the  clear 
solution,  in  case  filtration  was  not  necessary, 
until  it  is  saturated;  then  either  cool  the 
solution  rapidly  or  allow  it  to  stand  until  the 
next  exercise.  The  lead  nitrate  crystals  may 
be  filterd  on  an  ordinary  filter  or  on  a  Witt 
plate  and  dried  in  the  open  air.  If  the  amount 
of  mother-liquor  (filtrate)  is  considerable 
more  crystals  may  be  obtaind  by  continuing 
the  evaporation  of  the  liquid.  / 

NOTES  \ 

It  is  essential  that  the  apparatus  be 
clean.  If  sulfates  are  introduced  by  means 
of  the  measuring  cylinders  or  beakers 
white  insoluble  lead  sulfate  will  be  formd 
which  must  be  filterd  out.  If  commercial 
nitric  acid  is  used  it  may  contain  sulfuric  acid. 

If  the  litharge  does  not  all  dissolv  more 
nitric  acid  may  be  added  or  the  solution  may 
be  filterd  and  the  excess  litharge  discarded. 
An  excess  of  nitrate  ions  from  the  acid  re- 
duces the  solubility  of  the  lead  nitrate  in 
water  so  it  is  difficult  to  use  solubility  tables 
to  determin  the  least  volume  of  liquid  neces- 
sary to  hold  the  amount  of  lead  nitrate  pro- 
duced in  solution. 

The  amount  of  lead  nitrate  in  100  cc.  of  a 


40 


Preparation  of  Substances 


solution  saturated  at  given  temperatures  is 
found  in  the  following  table. 


Solubility  Table 


Temperature 

0° 

10° 

18° 

25° 

50° 

100° 

Pb(N03)2  grams 

36 

44 

51 

56 

79 

127 

Strength  of  Nitric  Acid  Solutions 


1  cc.  contains 

Density. 

nitric  acid, 

grams. 

1.05 

0.094 

1.10 

0.188 

1.15 

0.2177 

1.20 

0.388 

1.25 

0.486 

1.30 

0.617 

1.35 

0.753 

1.40 

0.914 

1.45 

1.121 

QUESTIONS 
(To  be  answerd  in  the  notebook.) 

1.  How  many  grams  of  lead  nitrate  could  be  made 
from  20  grams  of  litharge?  What  amount  of  boiling 
water  is  necessary  to  dissolv  this  amount  of  salt? 
(See  solubility  table.) 

2.  How  many  grams  of  lead  nitrate  did  you  make? 

3.  Is  the  salt  more  or  less  soluble  in  nitric  acid  than 
in  water?    Why? 

4.  How  many  cubic  centimeters  of  nitric  acid  of  a 
density  of  1.10  would  be  necessary  to  measure  out  if 
200  grams  of  actual  acid  were  required? 

5.  How  is  nitric  acid  made?  Explain  the  presence 
of  sulfuric  acid  in  commercial  nitric  acid. 


LEAD  ARSENATE 

Lead  arsenate  is  the  standard  arsenical 
poison  for  chewing  insects.  It  is  made  by 
mixing  equivalent  amounts  of  solutions  of 
either  lead  acetate  or  lead  nitrate  with  sodium 
arsenate. 

Calculation.  —  Inquire  as  to  the  character 
of  the  sodium  arsenate  available  —  as  to  its 
condition  of  hydration  and  degree  of  purity 
—  and  from  the  equation, 

Na^HAs04  •  7H2O  +  Pb(N03)2  =  PbHAs04 
+  2NaN03  +  7H2O, 

calculate  the  amount  of  disodium  hydrogen 
arsenate  that  will  be  necessary  to  react  with 
20  grams  of  lead  nitrate. 

If  the  salt  is  hydrous  the  7H2O  will  be  weighd  out 
and  must  be  calculated;  if  anhydrous  the  7H2O  must 
be  left  out  of  the  calculation.  If  the  salt  is  80  per  cent 
pure  the  amount  to  be  used  must  be  increased  by  divid- 
ing by  0.80. 

Dissolv  the  lead  nitrate  in  50  cc.  of  warm 
water  and  dilute  to  a  total  volum  of  350  cc. 
with  cold  water.  Similarly  dissolv  the  req- 
uisit  amount  of  arsenate  of  soda  in  a  little 
warm  water  and  dilute  to  350  cc.  with  cold 

41 


42  Preparation  of  Substances 

water.  Mix  the  two  solutions.  Test  the 
liquid  with  pieces  of  red  and  blue  litmus 
paper. 

As  the  precipitate  of  white  lead  arsenate 
settles  decant  the  clear  supernatant  liquid 
—  best  over  the  edge  of  the  beaker,  not  using 
the  lip  —  fill  the  beaker  with  fresh  water,  stir 
the  mixture  and  again  allow  the  precipitate  to 
settle.  Repeat  this  washing  until  the  soluble 
salts  are  removed,  and  the  precipitate,  be- 
coming colloidal  in  character  and  refusing  to 
settle  completely,  is  partially  dispersed  thru 
the  liquid. 

This  condition  being  reacht  allow  the  mix- 
ture to  stand  over  night,  so  that  as  much  as 
possible  of  the  lead  arsenate  will  settle  out, 
then  decant  most  of  the  liquid,  neglecting  the 
loss  of  the  comparatively  small  amount  of 
precipitate  in  colloidal  condition,  and  bring 
all  the  remaining  precipitate  gradually  onto 
one  15-cm.  filter  folded  in  the  ordinary  way. 
Allow  the  precipitate  to  drain  in  the  funnel 
for  several  days;  even  a  week,  as  a  rule,  is 
not  too  long. 

"When  the  amount  of  moisture  is  reduced 
to  about  50  per  cent  the  mass  will  separate 
easily  from  the  paper  and  should  be  handed 
in. 


Lead  Arsenate  43 

NOTES 

With  large  beakers  such  as  are  most  al- 
ways used  in  this  washing  process  it  is  an 
easy  matter  to  put  a  stirring  rod  thru  the 
bottom  or  sides  of  the  beaker.  The  student 
should  learn  to  stir  without  touching  the 
stirring  rod  to  the  beaker.  In  such  a  case  as. 
the  one  in  hand  the  stirring  is  best  done  by 
the  force  of  the  entering  wash  water. 

The  quality  of  the  sodium  arsenate  on  the 
market  varies  greatly.  The  best  grades  are 
crystallin  and  hydrated.  The  inferior  grades 
are  frequently  anhydrous,  massiv,  of  spongy 
appearance  and  carry  considerable  sodium 
carbonate  and  sulfate. 

If  the  two  salts  are  not  used  in  equivalent 
proportions  the  litmus  paper  will  show  which 
was  taken  in  excess.  Lead  nitrate  turns  the 
paper  red  while  sodium  arsenate  turns  it 
blue. 

The  washing  takes  out  the  excess  of  either 
salt  that  may  have  been  used,  and  the  sodium 
nitrate  formd  by  the  reaction.  In  the  pres- 
ence of  any  considerable  quantity  of  these 
salts  the  small  particles  of  lead  arsenate  are 
flocculated,  that  is,  many  thousands  are 
brot  together  in  one  floe.  As  the  concen- 
tration of  the  soluble  salts  is  lowerd  by  wash- 
ing the  particles  separate,  are  deflocculated. 


44  Preparation  of  Substances 

and  become  so  small  that  their  rapid  motion 
ofsets  the  force  of  gravity. 

The  rapid  motion  of  any  small  particle 
in  suspension  may  be  easily  observd  under 
a  high  power  microscope.  The  motion  is 
produced  by  the  molecules  of  water  which 
strike  the  larger  particles  with  sufficient  force 
and  frequency  to  keep  them  in  oscillation. 
This  motion  is  known  as  the  "  Brownian 
movement." 

The  action  which  the  arsenate  of  lead 
undergoes  in  becoming  colloidal  is  said  to 
be  as  follows:  When  the  soluble  salts  (elec- 
trolytes) are  sufficiently  decreased  by  the 
washing  process  some  groups  of  mole- 
cules of  lead  arsenate  react  with  either  the 
hydrogen  or  the  hydroxyl-ions  of  the  water 
combining  with  them.  If  the  particles  com- 
bine with  the  hydrogen  they  become  posi- 
tively charged  colloids  and  the  hquid  re- 
taining the  negativ  hydroxyl  group  becomes 
negativ.  It  is  entirely  possible  that  it  is 
the  layer  of  atoms  on  the  surfaces  of  the 
particles  of  arsenate  of  lead  which  is  active 
in  combining  with  either  the  H"^  or  the  ~0H 
of  the  water.  The  action  of  salt  in  coagu- 
lation, or  precipitation,  consists  in  neutraliz- 
ing the  electrical  charges.  As  this  takes 
place  the  lead  arsenate  particles,  which  were 
previously  all  of  the  same  electrical  condi- 


Lead  Arsenate  45 

tion  and  consequently  were  all  repellent  of 
each  other,  gradually  floe  together,  the 
Brownian  motion  slows  down,  and  as  the 
particles  continue  to  coalesce  the  Brownian 
motion  ceases  and  the  solid  separates  out  as 
a  precipitate. 

The  arsenate  of  lead  formd  is  a  mixture  of 
two  compounds;  one  acidic  having  the  sym- 
bol PbHAs04,  and  one  basic  represented  by 
the  formula  Pb3As204  •  Pb20HAs04.  These 
two  compounds  are  in  equilibrium, 

5PbHAs04  +  HOH  ^  Pb50H(As04)3 
+  2H3ASO4, 

the  acidic  one  being  gradually  changed  to  the 
basic  one  as  the  arsenic  acid  formd  in  the 
reaction  is  decanted  off  during  the  washings. 
The  change  to  the  basic  compound,  however, 
is  very  slow  as  with  very  slight  concentra- 
tions of  arsenic  acid  such  as  accumulate  in 
the  wash  water  the  action  stops  and  no  more 
basic  compound  is  formd  until  the  superna- 
tant wash  water  is  replaced  by  fresh.  As  an 
example  of  the  slowness  of  the  change  it 
required,  in  an  experiment  by  McDonnell 
and  Graham  of  Washington,  D.  C,  con- 
tinuous washing  for  a  year  to  change  two 
grams  of  the  lead  acid  arsenate  to  the  basic 
substance. 

A  piece  of  blue  litmus  paper  added  to  the 


46  Preparation  of  Substances 

mixture  after  the  material  has  been  well 
washt  will  turn  red  slowly  showing  the  pres- 
ence of  a  sUght  concentration  of  acid.  This 
is  the  arsenic  acid  hydrolyzed  oE  from  the 
acid  arsenate. 

The  addition  of  any  acid  changes  the 
equilibrium  from  right  to  left  forming  the 
acidic  arsenate  with  the  elimination  of  the 
basic  compound.  Most  of  the  lead  arsenate 
pastes  on  the  market  are  made  with  lead 
nitrate  and  the  acidity  of  the  system  is 
sufficient  to  produce  a  mixture  consisting 
mostly  of  the  acid  arsenate  with  smaller 
proportions  of  the  basic  compound. 

Inasmuch  as  the  acidic  arsenate  consists 
of  approximately  33  per  cent  AS2O5  and  the 
basic  approximately  23  per  cent  the  analysis 
of  the  compound  will  show  the  proportions 
of  the  two  arsenates  present.  For  example, 
a  mixture  of  the  two  analyzing  30  per  cent 
AS2O5  is  nearly  all  acidic  and  contains  very 
Httle  of  the  basic  compound,  while  one 
analyzing  28  per  cent  is  composed  of  equal 
parts  of  the  two  arsenates,  basic  and  acidic. 
These  facts  can  be  applied  to  the  analysis  of 
two  commercial  samples  of  arsenate  of  lead 
which  are  here  given,  one  made  from,  lead 
nitrate  which  contains  a  strong  acid  and  the 
other  made  from  lead  acetate  containing  a 
weak  acid. 


Lead  Arsenate 


47 


Analyses  of  Lead  Arsenate 


Made  from  lead 

nitrate,  per  cent  in 

dry  salt. 

Made  from  lead 

acetate,  per  cent  in 

dry  salt. 

AS205. . . . 

PbO 

31.40 
62.80 

25.40 
74.11 

It  will  be  seen  that  both  preparations  are 
mixtures  of  the  two  compounds,  the  one  made 
from  lead  nitrate  containing  much  more,  in 
fact  is  nearly  all,  of  the  acidic  compound 
PbHAs04,  while  the  one  made  in  the  presence 
of  less  acid  contains  a  large  proportion  of  the 
basic  compound. 

Most  of  the  arsenate  of  lead  on  the  market 
is  in  the  form  of  a  paste  containing  45  to  50 
per  cent  water,  consequently  the  actual  per 
cents  of  arsenic  and  lead  oxids  in  the  ma- 
terials would  be  about  one-half  the  figures 
just  given.  The  dry  powder  on  the  market 
is  said  to  be  made  by  an  entirely  different 
process,  by  suspending  lead  plates  in  arsenic 
acid  and  causing  chemical  action  by  means  of 
an  electric  current.  The  lead  arsenate  that 
falls  off  the  plates  has  only  to  be  washt  and 
dried. 

For  most  uses  lead  arsenate  replaced  Paris 
green  as  an  arsenical  poison.  Its  two  advan- 
tages are  its  greater  insolubility  and  its  ability 
to  stick.     The  solubility  of  lead  arsenate  in 


48  Preparation  of  Substances 

pure  water  is  extremely  slight.  It  is,  how- 
ever, readily  decomposed  by  the  salts  which 
appear  in  natural  waters,  the  carbon  dioxid  of 
hard  water  being  particularly  effective.  The 
amounts  of  arsenic  acid  set  free  by  this  reac- 
tion are,  generally,  less  than  one  per  cent, 
depending  on  the  water  used  and  not  enuf  to 
burn  foliage. 

QUESTIONS 
(To  be  answerd  in  the  notebook.) 

1.  How  many  grams  of  anhydrous,  80  per  cent 
pure,  arsenate  of  soda  would  be  required  to  put  with 
20  grams  of  lead  nitrate? 

2.  Explain  how  lead  nitrate  can  turn  litmus  red. 

3.  Similarly,  how  sodium  arsenate  can  turn  litmus 
blue. 

4.  What  is  meant  by  the  terms  flocculent;  de- 
flocculated? 

5.  Explain  the  action  of  soluble  salts  in  flocculating 
the  precipitate. 

6.  What  salts  are  washt  out  of  the  mixture?  How 
did  the  litmus  paper  act  in  your  preparation  im- 
mediately after  mixing? 

7.  How  much  arsenic  acid  (AS2O5)  in  an  ordinary 
lead  arsenate  paste? 

8.  If  lead  costs  more  than  arsenic  which  is  cheaper 
to  use  as  a  lead  salt,  the  nitrate  or  the  acetate?  The 
analyses  of  lead  arsenates  given  \^'ill  furnish  the  answer. 

9.  Calculate  the  per  cents  of  AsoOs  and  PbO  in 
PbHAs04  in  the  basic  compound.  This  will  be  confus- 
ing unless  the  student  keeps  in  mind  the  fact  that  the 
amount  of  two  arsenics  cannot  be  calculated  where 
only  one  exists,  i.e.,  AS2O5  cannot  be  calculated  from 


Lead  Arsenate  49 

one  molecule  PbHAs04,  whereas  it  can  from  two  mole- 
cules. In  other  words  the  student  is  askt  to  ecboIv 
2PbHAs04  into  2PbO,  AS2O5  and  HoO,  the  water  being 
neglected  in  this  case. 

10.   What  are  the  advantages  of  lead  arsenate  over 
Paris  green? 


LIME-SULFUR 

36-80-50  Formula 

Lime-sulfur  is  an  amber  colord  liquid  con- 
taining calcium  polysulfids,  CaS4  and  CaSs, 
and  some  calciimi  thiosulfate,  CaS203.  It  is 
made  by  boiling  lime  with  a  suspension  of 
suKur.  It  first  came  into  use  as  an  insecticide 
on  the  Pacific  coast  about  1900  to  combat  the 
San  Jose  scale.  Previous  to  that  time  a 
''Lime,  Sulfur  and  Salt"  mixture  had  been 
used  as  a  sheep  wash.  Nowadays  its  use  in 
more  dilute  solutions  is  extending  rapidly  to 
control  ''blights"  or  fungus  diseases,  while 
the  stronger  solution  is  still  one  of  the  stand- 
ard remedies  for  scale  insects.  In  the 
stronger  solutions  it  is  appl^ed  during  the  late 
winter  or  early  spring  before  the  buds  burst. 

Procedure.  —  Select  a  beaker  or  porcelain 
dish  of  400-500  cc.  capacity,  measure  into  it 
200  cc.  of  water,  and  mark  the  level  of  the 
liquid  so  that  the  mark  can  be  recognized 
after  the  dish  is  used  for  boiling.  Weigh  out 
38  grams  of  quicklime,  and  slake  it  in  the 
proper  amount  of  water.  Weigh  out  80 
grams  of  sulfur  flour  and  make  this  into  a 
thoroly  moistend  paste  with  about  200  cc.  of 

50 


Lime-Sulfur  51 

water.  Bring  the  ingredients  together  in 
the  markt  dish,  place  the  dish  on  a  piece  of 
asbestos  over  a  flame,  and  keep  the  mixture 
boiUng  gently. 

Dm-ing  the  boiUng  replace  the  water  if  it 
gets  near  the  200  cc.  mark.  It  is  not  neces- 
sary that  any  particular  volum  should  re- 
main at  the  end  of  the  boiling  period;  the 
less  water  the  stronger  the  solution  and  the 
more  thiosulfate  is  decomposed  and  the  more 
CaSs  is  formd  in  place  of  CaS4;  however,  if 
the  solution  is  made  too  concentrated  there 
will  not  be  sufficient  liquid  to  float  the 
hydrometer  spindle.  To  make  a  solution  of 
the  same  density  as  the  commercial  prepara- 
tions, 34°  Be.,  it  would  be  necessary  to  con- 
centrate the  liquid  to  less  than  200  cc. 

When  the  liquid  acquires  a  dark  amber 
color  and  the  suspended  sulfur  has  dis- 
appeard  the  lime-sulfur  is  made.  This  may 
require  an  hour.  If  the  preparation  is  to 
stand  until  the  next  exercise  it  should  be 
coverd  to  keep  out  as  much  oxygen  a^  pos- 
sible. Reducing  the  surface  by  placing  the 
mixture  in  a  narrow  vessel  also  reduces  the 
oxygen  absorption.  If  it  is  intended  to  com- 
plete the  work  at  once  the  mixture  may  be 
coold  by  immersing  the  container  in  water. 
After  standing  observe  that  a  crust  has 
formd  on  the  surface  of  the  hquid  which  is 


52  Preparation  of  Substances 

much  thicker  if  the  preparation  has  stood 
for  several  days.  Decant  the  clear  Hquid 
into  the  special  Ume-suifur  hydrometer  cyl- 
inders and  take  the  density  on  both  the 
specific  gravity  and  Beaume  scales.  From 
the  concentrated  clear  liquid  prepare  two 
sprays,  one  for  use  when  the  buds  are  dor- 
mant and  one  for  use  on  the  green  foliage 
in  summer.  Take  the  density  (Be.)  of  both 
diluted  sprays  and  record  the  data  in  the 
notebook. 

If  any  lead  arsenate  is  available  make  a 
thin  paste  of  this  and  add  some  of  it  to  the 
dilute  summer  spray.  Notice  the  gradual 
darkening  as  some  of  the  lead  is  withdrawn 
from  the  combination  with  arsenic  acid  and 
combined  with  sulfur  to  form  black  lead 
sulfid;  small  amounts  of  arsenic  acid  are  set 
free  at  the  same  time.  This  is  a  combination 
spray  having  two  functions,  insecticidal  and 
fungicidal. 

NOTES 

The  1910  Geneva  Formula,  36  pounds 
of  lim.e;  80  pounds  sulfur;  50  gallons  water, 
is  here  made  over  for  laboratory  use.  The 
directions  are  based  on  bulletin  No.  329 
of  the  New  York  Agricultural  Experiment 
Station,  by  Van  Slyke,  Bosworth  and  Hedges. 

If  the  lime  is  pure  36  grams  should  be  used, 
if  95  per  cent  CaO  (i.e.,  5  per  cent  MgO) 


Lime-Sulfur  53 

38  grams  should  be  used,  if  90  per  cent  lime 
40  grams.  Lime  that  is  over  10  per  cent 
magnesium  oxid  should  not  be  used  as 
it  is  a  waste  of  material.  The  magnesium 
forms  insoluble  compounds  that  go  into  the 
sediment.  In  case  the  lime  is  already  slaked 
increase  the  quantity  in  the  ratio  of  the 
weights  of  CaO  :  Ca02H2  (i.e.,  56  :  74). 

It  is  an  easy  matter  to  select  lime  that 
carries  less  than  2  per  cent  of  magnesia  as  the 
analysis  is  on  the  barrel  and  the  product  of  a 
given  '.ime-kiln  is  fairly  constant  in  compo- 
sition. 

If  all  the  material  is  not  in  very  finely 
divided  condition  it  will  remain  as  sediment 
and  not  react;  hence  the  sulfur  is  moistend 
to  prevent  lumping. 

If  a  beaker  is  used  place  a  piece  of  asbestos 
under  it,  otherwise  the  solid  material  will 
form  a  blanket  over  the  bottom  of  the  beaker 
and  prevent  the  diffusion  of  the  heat.  The 
glass  will  not  stand  sudden  local  heating  and 
cooling  resulting  from  such  blanketing. 

The  reactions  w^hich  take  place  when  the 
material  is  being  made,  according  to  Pro- 
fessor Tartar  at  the  Oregon  Agricultural  Ex- 
periment Station,  are,  first,  the  action  of  lime 
and  sulfur  to  form  calcium  tetrasulfid,  and 
calciima  thiosulfate, 

3Ca02H2  +  lOS  =  2CaS4  +  CaS203  +  3H2O. 


54  Preparation  of  Substances 

Second,  as  the  liquid  becomes  concentrated 
the  calcium  thiosulfate  breaks  down  forming 
the  insoluble  calcium  sulfite  liberating  one 
atom  of  sulfur, 

CaS203  =  CaSOs  -h  S. 

This  reaction  may  be  taking  place  in  this 
experiment  when  the  volume  of  the  liquid  is 
reduced  to  about  200  cc.  The  insoluble  cal- 
cium sulfite  remains  as  a  sediment.  Third, 
the  sulfur  liberated  from  the  thiosulfate  unites 
with  the  tetrasulfid  forming  pentasulfid, 

CaS4  -f  S  =  CaSo. 

Thus  the  composition  of  the  mixture 
changes  during  concentration.  The  amounts 
of  thiosulfate  and  tetrasulfid  become  lessend 
and  the  quantity  of  pentasulfid  increased. 
Such  changes  are  considerd  desirable  and 
have  been  effected  in  most  of  the  commercial 
preparations  on  the  market. 

Combination  sprays  may  be  made  by  mix- 
ing Ume-sulfur  with  arsenate  of  lead  or 
nicotine  sulfate,  or  both,  and  simultaneously 
kill  chewing  insects  and  aphis,  as  well  as 
prevent  attacks  of  fungus  diseases. 

Professor  Schaefer,  of  the  Michigan  Agri- 
cultural College,  states  that  the  action  of 
lime-sulfur  solution  upon  the  San  Jose  scale 
is  one  of  suffocation;   that  the  caustic  liquid 


Lime-Sulfur  55 

finds  its  way  under  the  edges  of  the  Httle 
shell  under  which  the  insect  lives,  shutting 
off  the  outside  oxygen  and  rapidly  con- 
suming what  remains  inside. 

The  fungicidal  action  of  lime-sulfm*  is 
thot  to  be  due  to  the  sulfur  deposited  from  it. 
This,  in  the  air,  oxidizes  slowly  to  sulfur 
dioxid  which  is  toxic. 

Long  boihng  exposed  to  the  air,  as  is  neces- 
sary in  laboratory  manipulation,  is  harmful 
to  the  product  as  the  polysulfids  react  rapidly 
with  the  oxygen  of  the  air  depositing  sulfur 
and  forming  thiosulfate, 

CaSs  +  30  =  CaSaOa  +  3S. 

This  is  the  change  that  takes  place  when 
hme-sulfur  stands  exposed  to  the  air.  At 
first  only  a  film  of  sulfur  is  seen  as  the  cal- 
cium thiosulfate  dissolvs,  but  as  the  upper 
layer  becomes  saturated  with  thiosulfate 
crystals  these  become  mixt  with  the  sulfur 
forming  a  hard  crust.  It  is  evident  from  this 
that  the  mixture  should  not  stand  in  the 
laboratory  any  longer  than  necessary. 

The  action  of  lime-sulfur  when  used  as  a 
spray  follows  from  the  explanation  in  the 
previous  paragraf.  First,  it  rapidly  takes 
up  oxygen  forming  calcium  thiosulfate  and 
depositing  all  the  sulfur  in  excess  of  two  atoms 
to    the    molecule.     Second,    the    thiosulfate 


56 


Preparation  of  Substances 


slowly  breaks  down  to  insoluble  sulfid  and 
one  atom  of  sulfur  is  set  free.  This  change 
is  slow  and  is  represented  by  the  equation, 

CaSsOs  =  CaSOs  +  S. 


Lime-Sulfur  Table  * 
Data  furnishing  a  basis  for  diluting  lime-sulfur  wash 


Dilution 

as  indicated  for 

Iga 

.  solution. 

Sulfur 

to 
1°B6.. 

Sulfur 

in  sol., 

per 

VVt.  one 
gal., 
lbs. 

Sulfur 

in  one 

gal.. 

Den- 
sity. 

Dormant 

Blister 

Sum- 

per 

ceat. 

lbs. 

spray. 

niiie 

mer 

cent. 

(San  ioa6 

gals. 
water. 

spray. 

scale), 
Tals.wate: 

gals, 
water. 

36 

0.75 

27.00 

11.08 

2.99 

9 

12^ 

45 

35 

0.75 

26.25 

10.98 

2.88 

8f 

12 

m 

34 

0.75 

25.50 

10.88 

2.77 

81 

lU 

411 

33 

0.75 

24.75 

10.78 

2.67 

8 

11 

40 

32 

0.74 

23.70 

10.69 

2.53 

7h 

lOi 

m 

31 

0.74 

22.95 

10.60 

2.43 

71 

10 

36i 

30 

"0.73 

21.90 

10.51 

2.30 

61 

9i 

341 

29 

0.73 

21.15 

10.42 

2.20 

6^ 

9 

32| 

28 

0.72 

20.15 

10.32 

2.08 

6 

81 

31 

27 

0.72 

19.45 

l'J.23 

1.99 

5f 

8 

29i 

26 

0.71 

18.45 

10.15 

1.87 

5i 

7h 

27f 

25 

0.70 

17.50 

10.07 

1.76 

5 

7 

26 

24 

0.69 

16.65 

9.98 

1.65 

41 

61 

24i 

23 

0.68 

15.65 

9.90 

1.55 

4i 

6 

22| 

22 

0.67 

14.75 

9.82 

1.45 

3f 

5^ 

2U 

21 

0.66 

13.85 

9.74 

1.35 

31 

5 

191 

20 

0.65 

13.00 

9.67 

1.26 

H 

4f 

18^ 

19 

0.65 

12.35 

9.59 

1.18 

3 

4| 

17 

18 

0.65 

11.70 

9.51 

1.11 

21 

4 

16 

17 

0.65 

11.05 

9.44 

1.04 

2h 

3f 

15 

16 

0.65 

10.40 

9.37 

0.97 

21 

31 

14 

15 

0.65 

9.75 

9.30 

0.90 

2 

3 

12| 

*  From  Bulletin  No.  329,  page  316,  New  York  Agri- 
cultural Experiment  Station;  Van  Slyke,  Bosworth  and 
Hedges. 


Lime-Sulfur  57 

Third,  the  sulfite  takes  up  oxygen  forming 
calcium  sulfate, 

CaSOa  +  0  =  CaS04, 

so  that  calcium  sulfate  and  sulfur  are  the 
final  products  of  decomposition  of  the  lime- 
sulfur  mixture. 

The  analysis  of  a  commercial  lime-sulfur 
concentrate  is  as  follows: 

Sp.gr.,  1.30  or  33.7  B^. 

Sulfur  in  thiosulfate, 0.25% 

Sulfur  in  tetrasulfid, 0.50% 

Sulfur  in  pentasulfid, 24.75% 

Total  sulfur, 25.50% 

This  shows  that  the  amount  of  thiosulfate 
has  been  greatly  reduced,  and  that  the  sub- 
stance present  in  greatest  quantity  is  cal- 
cium pentasulfid. 

QUESTIONS 
(To  be  answerd  in  the  notebook.) 

1.  Did  you  have  sufficient  lime-sulfur  solution  to 
float  the  hydrometer  spindle?  What  was  the  Beaume 
reading  of  your  solution? 

2.  How  many  pounds  of  sulfur  in  one  gallon  of  your 
solution? 

3.  How  much  would  the  suKur  in  50  gallons  cost 
at  the  rate  of  $20.00  per  ton? 

4.  What  dilution  did  you  make  for  the  Sian  Jose, 
scale?    What  was  the  density  of  the  dilute  solution? 


58  Preparation  of  Substances 

t 

5.  What  dilution  for  summer  spray?  Resulting 
density? 

6.  What  change  was  observd  when  lead  arsenate 
was  mixt  with  the  summer  spray?  What  new  in- 
soluble substance  was  formd? 

7.  What  is  the  per  cent  of  sulfur  in  the  lime-sulfur 
you  made? 

8.  What  substances  are  in  lime-sulfur?  Under- 
score the  one  present  in  largest  quantity. 

9.  What  is  in  the  sediment  in  lime-sulfur? 

10.  Write  the  reactions  that  take  place  when  the 
lime-sulfur  is  made,  placing  the  name  of  each  substance 
under  its  symbol. 

11.  Similarly  write  the  series  of  reactions  that  take 
place  when  lime-sulfur  is  oxidized. 

12.  What  effect  on  the  composition  of  lime-sulfur 
has  long  boiling?    The  concentration  below  200  cc? 

13.  What  are  the  uses  of  lime-sulfur? 

14.  What  is  said  to  be  the  action  of  lime-sulfur 
in  killing  San  Jose  scale? 

15.  What  are  the  final  products  of  oxidation  of 
lime-sulfur? 

16.  A  barrel  of  lime-sulfur  was  left  half  full  over  one 
season.  What  substances  would  be  found  in  the 
crust  that  formd  on  the  liquid? 

17.  What  specific  gravity  is  equivalent  to  33  B^.? 

18.  What  are  the  ordinary  impurities  in  lime? 

19.  Write  the  reaction  for  slaking  lime. 

20.  How  many  grams  of  slaked  lime  can  be  made 
from  40  grams  of  quicklime? 


COPPER    SULFATE 

Procedure.  —  Place  in  a  beaker  10  grams 
of  metallic  copper,  50  cc.  of  water,  15  to  18  cc. 
of  chamber  sulfuric  acid  and  25  cc.  of  dilute 
(sp.  gr.  1.2,  32  per  cent)  nitric  acid.  Place 
the  mixture  on  asbestos,  under  a  hood,  and 
heat  gently  with  a  low  flame  until  the  copper 
is  all  dissolvd.  This  should  require  about 
an  hour.  In  case  the  solution  becomes 
saturated  during  the  heating  as  evinst  by 
the  crystals  forming  on  the  surface,  add  a 
few  drops  of  water.  When  the  copper  is  all 
dissolvd  continue  heating  until  the  solution  is 
saturated,  then  remove  the  beaker,  place  it 
in  cold  water  and  stir  the  solution  as  it  cools 
until  crystalUzation  is  complete.  Filter  off 
the  crystals  on  a  Witt  plate.  Evaporate 
the  filtrate  to  the  point  of  crystallization  and 
cool  the  liquid  until  all  the  crystals  have 
formd  that  will.  If  possible  pour  out  the 
mother  liquor,  which  consists  mostly  of  strong 
acids,  and  bring  the  remaining  crystals  onto 
a  Witt  filter.  Put  both  crops  of  crystals  into 
25  cc.  of  boiling  water  and  adjust  the  quan- 
tity of  water,  by  adding  directly  and  boiling 
off,  until  the  salt  is  all  dissolvd  and  the  solu- 

59 


60  Preparation  of  Substances 

tion  becomes  saturated.  Cool  the  liquid 
with  stirring  or  allow  it  to  stand  until  the 
next  exercise.  Filter  off  the  crystals  and  dry 
them  between  filter  paper.  Save  the  mother 
liquor  for  the  tests  which  follow. 

Tests  for  copper ;  Notebook.  —  Test  some 
copper  sulfate  by  adding  ammonium  hy- 
droxid,  at  first  one  drop,  then  in  larger  quan- 
tity. The  light  blue  insoluble  substance 
f  ormd  by  the  small  amount  of  ammonia  is  a 
basic  copper  sulfate;  the  blue  solution  con- 
tains copper  and  ammonia  together  in  one 
ion,  an  ammonio-cupric  sulfate  Cu(NH3)4S04. 
This  solution  contains  very  few  copper  ions  — 
only  those  that  break  away  from  this  com- 
plex. The  formation  of  a  blue  solution  is  a 
test  for  copper.  To  the  blue  solution  add  a 
few  drops  of  potassium  ferrocyanide.  There 
being  so  few  Cu  ions  the  copper  ferrocyanide 
formd  is  not  v  sible.  Break  up  the  ammonio- 
copper  complex  by  adding  acetic  or  dilute 
hydrochloric  acids.  As  soon  as  copper  ions 
are  present  in  amount  of  about  0.002  per  cent 
the  copper  ferrocyanide  begins  to  be  visible. 

Add  a  few  drops  of  potassium  ferrocyanide 
to  a  copper  sulfate  solution.  The  formation 
of  brown  copper  ferrocyanide  is  a  test  for 
copper. 


Copper  Sulfate  61 

NOTES 

Bluestone  or  copper  sulfate  is  the  impor- 
tant salt  of  copper  for  agriculture.  Its  weak 
solution  is  fungicide  and  a  disinfectant. 
Seed  wheat  is  treated  with  it  to  kill  the 
spores  of  the  smut.  Bordeaux  mixture  and 
Paris  green  are  made  from  it. 

Copper  does  not  dissolv  in  acids  without 
first  being  oxidized.  This  may  be  accom- 
pHsht,  superficially,  by  heating  in  air  when 
the  resulting  coating  of  black  copper  oxid 
will  dissolv  in  sulfuric  acid.  Copper  may  be 
fused  with  sulfur  when  the  resulting  copper 
sulfid  will  respond  to  the  action  of  sulfuric 
acid.  The  unreduced  copper  sulfid  of  copper 
matte  which  falls  to  the  bottom  of  the  tank 
when  crude  copper  is  electrolytically  purified 
is  used  to  make  copper  sulfate.  Copper 
moistend  with  acid  will  take  oxygen  from  the 
air  and  dissolv  slowly.  In  this  experiment 
the  oxygen  is  obtaind  from  nitric  acid. 

QUESTIONS 
(To  be  answerd  in  the  notebook.) 

1.  From  the  sjTnbol,  CUSO4  •  5H2O,  calculate  the 
amount  of  crystallized  salt  that  may  be  made  from  10 
grams  of  metaUic  copper. 

2.  From  the  same  symbol  find  out  how  many  grams 
of  suKuric  acid  would  be  necessary. 

3.  Consult  the  table  of  the  density  of  sulfuric  acid 
under  superphosphate  and  determin  how  many  cubic 


62  Preparation  of  Substances 

centimeters  of  sulfuric  acid  would  be  necessary  to 
contain  the  number  of  grams  found  under  2. 

4.  What  volum  of  nitrogen  oxids  was  given  off  in 
this  experiment?  To  solv  this  problem  it  will  be 
necessary  to  establish  the  relationship  between  the 
weight  of  copper  used  and  the  volum  of  gas  given  off. 
The  gas  given  off  is  the  colorless  nitric  oxid  wliich 
changes  to  the  brown  nitrogen  dioxid  without  change 
in  volum  upon  exposure  to  the  air.  The  following 
equatioQ  shows  the  decomposition  of  nitric  acid  as  it 
takes  place  in  the  experiment, 

4HXO3  =  2H2O  +  3O2  +  4N0. 

The  change  from  the  colorless  to  the  brown  oxid  is 
simple, 

2N0  +02=  2NO2, 

and  the  quantities  2N0  and  2NO2  bear  out  the  state- 
ment that  there  is  no  change  in  volum  in  the  oxida- 
tion of  nitric  oxid  to  nitrogen  dioxid.  The  relation  of 
the  nitrogen  dioxid  to  the  copper  must  be  sought  thru 
the  oxygen  which  unites  w^th  the  copper, 

Cu  +  0  =  CuO. 

The  copper  being  once  oxidized  we  lose  interest  in  it, 
for  the  purposes  of  this  calculation,  as  it  reacts  with 
the  sulfuric  acid  without  changing  its  relationship  to 
the  oxygen, 

CuO  +  H2SO4  •  aq.  =  CUSO4  •  aq. 

Now  it  is  possible  to  establish  the  relationship  of  the 
copper  to  the  nitrogen  dioxid  thru  the  oxj^gen  as  fol- 
lows: One  Cu  unites  with  one  O,  hence  6Cu  unites 
wath  3O2  and,  from  the  first  equation,  the  produc- 
tion of  3O2  is  accompanied  by  the  evolution  of  4N0 
which  goes  to  4NO2  without  change  in  volum.  Then 
6Cu   are   accompanied    by  the    production    of   4NO2 


Copper  Sulfate  63 

which  estabhshes  the  relationship  between  the  copper 
and  the  gas  given  off.  The  number  of  giams  repre- 
sented by  the  symbol  NO2  occupies  22.4  hters  (molec- 
ular volum).  Now  we  have  the  complete  data  for  the 
ratio  which  is 

6Cu  381.6  grams  of  copper 


4(22.4  hters)  89.6  liters  of  gas 

As  10  grams  of  copper  were  used  in  the  experiment  the 
following  proportion  will  give  the  number  of  hters  of 
gas  produced: 

?51^  =  12  =  Uters  of  either  NO  or  NO2. 
89.6        X 

5.  What  is  necessary  to  make  copper  dissolv  in 
acids? 

6.  What  are  the  uses  of  copper  sulfate? 

7.  What  are  two  tests  for  copper?  What  compound 
in  each  case  is  used  to  recognize  the  copper? 

8.  How  can  the  number  of  copper  ions  in  a  solution 
be  reduced  to  a  negligible  quantity? 

9.  What  oxid,  or  oxids,  of  nitrogen  are  red?  What 
colorless? 

10.  How  many  liters  of  nitrogen  dioxid  were  given 
off  in  this  experiment?  Of  nitric  oxid  oxidized  by  the 
air?     How  many  grams  of  each? 


PARIS    GREEN 

Paris  green  closely  approximates  the  for- 
mula Cu(C2H302)2  •  3Cu(As02)2,  which  was 
assignd  it  by  Ehrmann  in  1834,  and  is  cald 
an  aceto-arsenite  of  copper.  There  are  two 
general  processes  for  making  it,  first  replacing 
most  of  the  acetate  ion  of  copper  acetate  by 
the  arsenite  ion  of  arsenious  acid ;  and  second, 
replacing  some  of  the  arsenite  ion  of  copper 
arsenite  by  the  acetate  ion  of  acetic  acid. 
The  latter  process  is  followd  in  these  direc- 
tions. 

Procedure.  —  Dissolv  9  grams  of  dry 
carbonate  of  soda,  or  24  grams  of  hydrous,  in 
a  beaker  or  porcelain  d'sh  in  80  cc.  of  water. 
Into  this  solution  sprinkle  gradually  16 
grams  of  arsenious  oxid,  and  boil  until  the 
acid  has  united  with  the  soda  as  shown  by 
solution  of  the  resulting  sodium  arsenite. 

Dissolv  20  grams  of  copper  sulfate  in  80 
cc.  of  water.  When  both  of  the  solutions 
are  at  about  60°  —  as  warm  as  the  hand  can 
comfortably  bear  —  pour  the  sodium  arsenite 
solution  into  the  copper  sulfate.  Add  10.5 
cc.  of  50  per  cent  acetic  acid  —  or  an  equiva- 
lent of  any  other  strength,   and  allow  the 

64 


Paris  Green  65 

mixture  to  digest  at  about  50°  for  some  time 
on  a  piece  of  asbestos  board  over  a  low  flame. 
If  the  green  copper  aceto-arsenite  does  not 
form  at  this  point,  not  enough  acetic  acid 
has  been  added.  Consult  an  Instructor 
before  adding  more  than  a  few  drops  of  acid 
as  too  much  may  decompose  the  salt.  Stir 
occasionally  —  once  in  five  minutes  —  and 
when  the  reaction  seems  complete  drain  the 
green  product  on  a  funnel  and  wash  to 
remove  soluble  arsenites  and  sodium  sulfate. 
Examin  the  size  and  shape  of  the  particles 
under  a  microscope.  When  dry  put  in  a 
clean,  dry  beaker  and  see  if  it  ''flows"  well. 

NOTES 

Paris  green  is  one  of  the  oldest  arsenical 
insecticides.  For  many  years  it  was  the 
standard  remedy  for  the  potato  beetle.  It 
is  applied  to  the  vines  suspended  in  water. 

The  composition  of  Paris  green  required 
by  the  symbol  is  never  exactly  attaind,  the 
amount  of  arsenic  being  somewhat  less  than 
the  ideal  quantity.  The  analysis  of  a  theo- 
retical compound  of  the  formula  given,  of 
two  samples  of  Paris  green  carefully  made, 
and  the  average  analysis  of  494  samples 
bot  on  the  open  market  in  Pennsylvania,  are 
given  in  the  following  table : 


66 


Preparation  of  Substances 


Analyses  of  Paris  Green 


AS2O3 

CaO 

(CH3)2(CO).0 
H2O 


Theoretical. 

Avery, 
Nebraska. 

Holland 
and  Reed, 
Massachu- 
setts. 

58.55 
31.39 
10.06 

57.55 
31.75 
10.31 

56.94 

31.74 

10.37 

0  78 

100.00 

99.61 

99.83 

Ke'loe;, 
average  494 

samples, 
Penn.,  1910. 


57.97 

29.41 


It  is  noticed  that  while  the  arsenic  falls 
about  one  per  cent  short  the  amount  of  copper 
oxid  is  slightly  increased  as  is  the  acetic  aiud, 
th's  may  be  taken  to  mean  that  there  is 
slightly  more  copper  acetate  in  the  compound 
than  is  shown  by  the  symbol. 

In  the  solution  from  which  Paris  green  is 
made,  arsenite,  acetate  and  copper  ions  must 
be  in  such  concentrations,  and  the  tempera- 
tures so  adjusted  as  to  allow  the  formation 
of  the  copper  aceto-arsenite.  Too  much 
acetic  acid  will  throw  the  white  arsenious  oxid 
out  of  solution.  The  reagents  must  be 
measured  with  considerable  care  to  avoid  the 
effect  of  varying  masses.  The  base  and  acids 
concernd  are  all  weak,  and  the  compound  is 
easily  hydrolyzed  by  water;  hence  the  long 
digestion  to  allow  the  formation  of  large 
particles  in  which  the  ratio  of  mass  to  surface, 
m/s,  is  greater. 


Paris  Green  67 

QUESTIONS 
(To  be  answerd  in  the  notebook.) 

1.  Name  the  acidic  and  basic  ions  used  in  making 
Paris  green. 

2.  What  shaped  particle  has  the  largest  ratio  of  m/s'i 

3.  What  are  the  relativ  advantages  of  Paris  greens 
composed  of  large  particles;  of  small  particles;  of 
particles  of  spherical  shape;  of  broken  cornered  par- 
ticles? (Discuss  in  reference  to  degree  of  hydrolysis 
and  time  of  suspension.) 

4.  What  is  the  objection  to  putting  Paris  green  in 
water  several  days  before  using?  Of  applying  on  a  wet 
day? 

5.  How  many  grams  of  crystallized  sodium  carbon- 
ate, Na2CO3*10H2O,  could  be  made  from  10  grams  of 
the  anhydrous  salt? 

6.  Water  hydrolyzes  Paris  green.  State  some  of 
the  possible  products  of  hydrolysis.  Which  of  these 
are  soluble? 

7.  Write  a  symbol  for  orthoarsenious  acid;  meta- 
arsenious  acid.     (See  textbook.) 

8.  Write  a  reaction  between  Na2C03  and  AS2O3 
naming  all  the  substances. 

9.  Write  the  s^nnbol  of  acetic  acid. 

10.   How  many  grams  of  arsenic  trioxid  will  react 
with  24  grams  of  dry  sodium  carbonate? 


BORDEAUX   MIXTURE 

I.   ORDINARY  BORDEAUX 

The  composition  of  the  mixture  produced 
by  the  formula  ordinarily  used,  4-4-50,  is 
said  to  be  a  basic  sulfate  of  copper  and  lime; 
its  composition  being  represented  by  the 
symbol,  CuS04.9CuO.CaS04-3CaO. 

Procedure.  —  Weigh  out  8  grams  of  cop- 
per sulfate,  dissolv  it  in  50  cc.  of  water,  using 
heat  if  it  is  desired  to  hasten  the  solution,  and 
add  350  cc.  of  cold  water  making  the  total 
volum  400  cc.  Slake  8  grams  of  quickhme 
with  a  little  water,  dilute  the  paste  with  about 
200  cc.  of  cold  water  and  strain  the  mass  thru 
a  piece  of  cheesecloth  placed  over  a  funnel 
or  a  thistle  tube.  Dilute  the  milk  of  lime  to 
400  cc.     Mix  the  cold  solutions. 

n.  WOBURN  BORDEAUX 

Woburn  Bordeaux  may  consist  of  either 
of  three  basic  sulfates  of  copper,  the  pro- 
portions of  base  to  acid  in  each  being  shown 
in  the  following  formulas:  CuS04«3CuO;  or 
CuS044CuO;  or  CuS04.9CuO.CaS04.  Its 
most   striking  characteristic   is  the  absence 

of  any  free  lime.     Either  of  the  three  com- 

68 


Bordeaux  Mixture  69 

pounds  may  be  made  in  this  experiment  ac- 
cording to  the  amount  of  Hme-water  used. 

Procedure.  —  Weigh  out  0.5  gram  of 
copper  sulfate  or  get  a  solution  containing 
that  amount  and  dilute  it  to  380  cc.  Meas- 
\xre  out  either  70,  74  or  84  cc.  of  Hme-water 
and  dilute  it  to  380  cc.  Mix  the  two  solu- 
tions. 

Properties  of  Bordeaux  Mixtures;  Note- 
book. 

1.  Compare  the  color  of  the  two  mixtures. 

2.  Stir  them  up  and  allow  to  stand.  Which  stays 
in  suspension  best? 

3.  How  much  does  each  mixture  settle  in  15  min- 
utes? Is  a  white  scimi  to  be  seen  on  either  prepara- 
tion?   If  so  which  one? 

4.  Filter  some  of  the  Woburn  Bordeaux  and  add 
a  few  drops  of  potassium  ferrocyanide  solution  to  test 
tube  of  the  clear  filtrate.  If  copper  is  in  solution  as 
positiv  ion,  in  amounts  of  over  0.002  per  cent,  the 
brownish  color  of  copper  ferrocyanid  should  be  seen. 
It  may  be  necessary  to  look  down  the  colum  onto  a 
white  background  to  see  the  color  and  it  may  be  well 
to  compare  this  tube  with  another  containing  only 
water  and  the  same  number  of  drops  of  ferrocyanid 
solution.     Are  any  copper  ions  (Cu+^")  in  solution? 

NOTES 

The  ordinary,  or  one  per  cent,  Bordeaux 
is  made  from  4  pounds  of  copper  sulfate, 
4  pounds  of  quicklime  and  50  gallons 
of  water.     This  formula  is  here  reproduced 


70  Preparation  of  Substances 

en  a  small  scale  suitable  for  laboratory  pur- 
poses. The  Woburn  Bordeaux,  if  enlarged 
to  barrel  proportions,  would  consist  of  4|- 
ounces  of  copper  sulfate,  4|  gallons  of  lime- 
water  in  51  gallons  of  the  mixture. 

Several  compounds  of  copper  can  be  made 
by  mixing  lime  and  copper  sulfate  in  different 
amounts.  The  following  symbols*  show  the 
proportions  present  in  the  various  substances 
that  can  be  formd: 

(I)  CuS04.3CuO.  (II)  CuS044CuO. 
(Ill)  CuS04.9CuO.CaS04.  (IV)  CUSO4. 
9CuO.CaS04-3CaO.       (V)    CuO-SCaO. 

It  will  be  noted  that  the  compound  (II)  is 
more  basic  than  (I)  and  that  the  basicity 
increases  progressively  so  that  (V)  is  all  base. 
The  compounds  are  produced  successively, 
by  using  increased  quantities  of  lime-water 
with  the  same  amount  of  copper  sulfate. 
For  example,  with  0.5  gram  of  copper  sulfate, 
70  cc.  of  lime-water  will  produce  the  com- 
pound CuS04'3CuO,  74.1  cc.  of  lime-water 
will  give  CuS04-4CuO  and  83.3  cc.  of  lime- 
water  will  make  CuS04.9CuO.CaS04.  Wo- 
burn Bordeaux  may  be  any  one  of  these 

*  Taken  from  the  11th  Annual  Report  (p.  25)  of  the 
Woburn  Experimental  Fruit  Farm  by  the  Duke  of  Bed- 
ford and  Mr.  Pickering.  Some  calcium  sulfate  is  reported 
united  with  the  first  three  compounds  in  addition  to  that 
represented. 


Bordeaux  Mixture  71 

compounds  or  mixtures  of  them.  With  a 
large  excess  of  the  base  the  compound 
(IV)  is  produced  having  the  formula 
CuS04-9CuO.CaS04-3CaO.  This  is  stiU 
more  basic  in  that  it  contains  some  of  the 
basic  calcium  sulfate  in  addition  to  the  basic 
copper  suKate.  Such  a  compound  the  ordi- 
nary Bordeaux  mixture  is  said  to  be. 

From  the  symbol  of  the  copper  compound 
in  ordinary  Bordeaux,  CuS04-9CuO-CaS04' 
3CaO,  an  equation  may  be  written  to  account 
for  the  formation  of  such  a  substance, 

IOCUSO4  +  12Ca02H2  =  CuS04-9CuO. 
CaS04-3CaO  +  8CaS04  +  I2H2O. 

From  this  it  is  seen  that  considerable  cal- 
cium sulfate  is  formd  at  the  time  the  Bor- 
deaux is  made.  Calcium  sulfate  is  soluble 
in  water  at  25°,  to  the  amount  of  0.21  gram 
per  Uter.  If  any  free  lime  is  left  over,  which 
is  always  the  case,  the  solubihty  is  lessend, 
as  both  compounds  contain  a  coromon  cal- 
cium ion. 

A  rough  calculation  on  the  part  of  the 
student  will  show  that  8  grams  of  copper 
sulfate  require  about  2  grams  of  lime  to 
react  with  it.  For  example,  the  formula  for 
the  precipitate  in  ordinary  Bordeaux  is 
given  as  CuS04-9CuO.CaS04-3CaO.  Lime  is 
used  to  produce  the  9CuO  and  the  3CaO 


72  Preparation  of  Substances 

making  12CaO  used  for  every  lOCu;  or 
more  in  detail,  9Ca02H2  were  necessary  to 
react  with  9CuS04  before  the  resulting 
9CUO2H2  could  form  9CuO  and  3CaO  are 
found  in  the  product  making  a  total  of  12CaO 
required.  The  lOCu  come  from  10CuSO4- 
5H2O  and  thus  the  ratio  between  copper 
sulfate  and  lime,  10CuSO4-5H2O/12CaO,  is 
estabUsht.  In  figures  it  is  2497.3/672  or 
3.7  showing  that  nearly  four  times  as  much 
Hme  is  used  as  is  cald  for  by  the  symbol. 
This  ratio  has  been  fixt  by  horticultural 
practise. 

From  the  previous  paragraf  it  is  evident 
that  nearly  four  times  as  much  hme  is  used 
as  is  needed.  The  student  will  inquire  as  to 
what  becomes  of  the  remainder.  The  solu- 
bnity  of  calcium  hydroxid  at  25°  is  0.16 
gram  in  100  cc.  of  water.  This  amount, 
however,  is  lessend  by  the  presence  of  cal- 
cium sulfate  so  that  only  a  small  portion  of 
the  whole  amount  of  lime  dissolvs  in  water. 
Further,  not  all  the  lime  weighd  out  gets 
into  the  preparation,  as  lumps,  air-slaked 
material  and  frequently  lime  itself  may  be 
rejected  by  the  strainer.  It  is  obvious  that 
all  the  lime  not  in  solution  must  be  mixt  in 
with  the  precipitate. 

The  white  scum  is  calcium  carbonate 
made  up  of  carbon  dioxid  from  the  air  and 


Bordeaux  Mixture  73 

the  excess  lime  in  solution.  There  must  be 
lime  enuf  present  to  precipitate  all  the  cop- 
per before  there  can  be  any  left  over  to 
react  with  carbon  dioxid  so  that  the  forma- 
tion of  a  white  scum  is  proof  that  no  copper 
remains  in  solution  and  that  the  mixture 
does  not  contain  any  soluble  copper  that  can 
burn  fohage. 

Bordeaux  mixture  protects  plants  from 
attacks  of  fungous  diseases.  When  spread 
over  the  leaf  it  dissolvs  very  slightly  and 
disease  spores  blown  on  by  the  wind  are 
kild  upon  germination  by  the  soluble  copper 
formd. 

The  substances  which  act  upon  the  Bor- 
deaux to  make  the  copper  soluble,  to  the  best 
of  our  present  knowledge,  are  the  carbon 
dioxid,  the  ammonia  and  the  nitric  acid 
present  in  the  atmosphere.  The  carbon 
dioxid  first  combines  with  hme  forming  in- 
soluble calcium  carbonate  and  following  this 
begins  the  conversion  of  the  copper  to  basic 
copper  carbonate  which  is  accompanied  by 
the  Hberation  of  copper  sulfate.  Basic  cop- 
per carbonate  is  dissolvd  by  more  carbon 
dioxid,  by  ammonia,  by  nitric  acid,  or  by 
ammonium  nitrate  made  from  the  ammonia 
and  nitric  acid.  The  amount  of  soluble  cop- 
per produced  by  the  atmospheric  agencies 
is   very   small,  —  thousandths   or   ten-thou- 


74  Preparation  of  Substances 

sandths  of  one  per  cent,  —  while  the  amount 
of  soluble  copper  that  a  leaf  can  stand  without 
burning  is  much  larger  and  is  in  the  neigh- 
borhood of  0.04  per  cent. 

The  ordinary  Bordeaux  mixture  —  con- 
taining four  times  as  much  lime  as  is  needed 
for  producing  the  insoluble  copper  compounds 
—  after  being  spread  out  on  the  plant  does 
not  begin  the  liberation  of  soluble  copper  until 
the  carbon  dioxid  of  the  atmosphere  has 
acted  on  the  excess  of  lime  present.  This 
process  requires  several  days.  On  the  other 
hand  the  Woburn  Bordeaux  having  no  excess 
of  lime  is  acted  upon  by  the  carbon  dioxid 
at  once  and  soluble  copper  is  available  in  a 
short  time. 

The  increased  vigor  of  plants,  particularly 
potatoes,  which  is  noticed  when  they  have 
been  sprayd  with  Bordeaux  mixture,  is  due, 
to  the  best  of  our  knowledge,  to  the  preven- 
tion of  minor  insect  ravages  rather  than  a 
stimulating  action  of  the  very  dilute  copper 
solution  on  the  chlorophyl.  It  has  been 
shown  by  Pickering  that  potato  leaves  im- 
merst  in  dilute  copper  sulfate  solution  give 
off  iron  and  take  on  copper  and  from  this  it 
was  argued  that  the  dilute  copper  solution 
might  have  an  accelerating  effect  upon  the 
chlorophyl  action.  Recent  work  has  shown, 
however,  that  the  simpler  explanation  of  in- 


Bordeaux  Mixture  75 

sect  and  disease  prevention  is  the  more 
plausible  explanation  of  the  apparent  stimu- 
lation. Iron  is  a  constituent  of  chlorophyl. 
The  rate  at  which  Bordeaux  mixture  settles 
is  an  important  matter.  Each  of  the  com- 
pounds I  to  V  has  a  different  density,  is  more 
or  less  voluminous  and  settles  at  a  different 
rate  from  the  others.  Pickering  states  that 
the  volums  occupied  by  the  precipitates  after 
standing  15  minutes  vary  regularly  and  may 
be  represented,  approximately,  by  these  num- 
bers, 8(1),  17(11),  86(111),  98(IV)*',  20(interpo- 
lated)  (V).  This  means  that  (IV),  ordinary 
Bordeaux,  is  the  most  voluminous  and  stays 
in  suspension  best.  Butler*  shows  that  the 
order  of  mixing  and  the  concentration  of  solu- 
tions at  the  time  of  mixing  have  a  bearing 
on  length  of  time  the  precipitate  stays  in  sus- 
pension and  reconmiends  making  a  dilute 
copper  solution  and  pouring  this  into  a  strong 
milk  of  lime.  The  directions  for  this  exercise 
allow  the  student  to  make  the  copper  and  lime 
solutions  of  equal  volum  and  pour  one  into 
the  other  indiscriminately.  According  to 
Butler  the  methods  followd  in  this  exercise 
take  second  rank  in  producing  desirable  volu- 
minous precipitates. 

*  Technical  Bulletin,  No.  8,  New  Hampshire  Experi- 
ment Station;  also  Phytopathology,  1914. 


76  Preparation  of  Substances 

QUESTIONS 

(To  be  answerd  in  the  notebook.) 

5.  What  amounts  of  copper  sulfate  and  lime-water 
did  you  use  in  making  your  Woburn  Bordeaux? 

6.  How  many  times  as  much  copper  sulfate  is  used 
for  ordinary  Bordeaux  as  for  the  Woburn  mixture? 
How  does  the  ordinary  Bordeaux  mixture  differ  in 
composition  from  Woburn? 

7.  Give  a  definition  for  a  basic  salt. 

8.  How  may  one  test  for  copper? 

9.  What  is  meant  by  the  expression  4-4-50? 

10.  The  symbol  for  the  compound  (I)  CuS04-3CuO 
may  be  written  4CuO*S03.  Re^vrite  (H),  (HI)  and 
(IV)  in  a  similar  manner.  Underscore  the  least  basic 
of  these  compounds.  Double  underscore  the  basic 
part  of  this  compound. 

11.  What  is  the  use  of  Bordeaux  mixture?  How 
does  it  act? 

12.  Figure  the  amount  of  calcium  sulfate  produced 
when  the  Bordeaux  is  made  using  the  ratio,  IOCUSO4: 
8CaS04,  in  the  equation  given  in  the  notes.  At  a 
volum  of  800  cc.  what  is  the  maximum  amount  that 
could  dissolv?  How  much  would  be  left  undissolvd? 
Is  the  undissolvd  portion  present  in  Bordeaux  mixture? 

13.  How  much  lime  is  used  in  this  experiment? 
How  much  is  used  in  the  reaction?  How  much  dis- 
solvs  in  water?      What  becomes  of  the  remainder? 

14.  What  substances  are  in  the  solid  part  of  the 
Bordeaux?    What  substances  are  in.  solution? 

15.  Did  you  observ  the  formation  of  a  thin  white 
scum  on  the  surface  of  the  ordinary  Bordeaux?  Ex- 
plain what  it  is  and  how  it  was  formd.  Write  the 
equation  showing  its  formation. 

16.  What  substances  cause  the  copper  to  dissolv 
from  the  Bordeaux  mixture? 


Bordeaux  Mixture  ■    77 

17.  What  is  meant  by  copper  in  a  positiv  ion? 
Copper  in  a  negativ  ion? 

18.  In  which  ion  is  the  copper  in  copper  sulfate? 
Positiv  or  negativ? 

19.  Why  is  the  hberation  of  soluble  copper  salt 
from  Bordeaux  delayd  by  the  presence  of  lime? 

20.  How   strong   a   solution   of   copper   sulfate   is 
necessary  to  kill  fungous  spores?     To  kill  plants? 


EMULSIONS 

An  emulsion  contains  two  immiscible 
liquids  and  a  third  colloidal  substance  mis- 
cible  to  a  greater  or  less  degree  with  each  of 
the  other  two  substances. 

I.   KEROSENE  EMULSION 

Procedure.  —  Weigh  5  grams  of  ordinary- 
yellow  soap  cut  into  pieces  to  aid  solution  and 
dissolv  by  the  aid  of  heat  in  40  cc.  of  water  in 
beaker.  When  solution  is  complete  add  80 
cc.  of  kerosene  and  stir  vigorously,  or  pour 
from  one  beaker  to  another,  until  the  emul- 
sion is  complete  as  evinst  by  the  disap- 
pearance of  the  oil.  This  is  a  stock  solution 
wh'-ch  is  diluted  with  2-10  parts  of  water  as 
required. 

Notebook. 

1.  Dilute  some  of  the  emulsion  and  examin  a  drop 
under  the  microscope.     What  is  seen? 

2.  What  substance  mixes,  to  a  slight  extent,  with 
both  the  kerosene  and  the  water? 

3.  Would  the  decomposition  of  this  substance 
destroy  the  emulsion?  Verify  by  experiment  and  tell 
how  it  was  done. 

4.  How  long,  upon  standing,  before  kerosene  sepa- 
rates? 

78 


Emulsions  79 

n.   MISCIBLE  OILS 

There  are  preparations  on  the  market 
which  contain  various  oils  with  the  emulsify- 
ing agent  already  added.  These  are  ready 
to  use  after  the  addition  of  water. 

Procedure.  —  Making  sure  that  all  the 
apparatus  used  is  clean,  get  10  cc.  of  a 
miscible  oil  and  dilute  it  with  12  volums  of 
water.  If  free  oil  appears  on  the  surface 
after  standing  a  minute  clean  the  apparatus 
once  more  and  repeat  the  experiment. 

NOTES 

Kerosene  emulsion  is  an  old  remedy  for  in- 
sects that  do  not  chew  and  consequently  can- 
not be  poisond.  Such  sucking  insects  have 
to  be  attackt  thru  their  breathing  apparatus. 
The  aphis  is  an  example.  Kerosene  alone  will 
burn  foUage  badly.  The  emulsion  allows  the 
use  of  so  httle  kerosene  that  no  harm  is  done 
the  foliage,  there  still  being  sufficient  to  de- 
stroy the  insect.  In  pract  se  the  happy 
medium  is  sometimes  hard  to  reach.  Kero- 
sene emulsion  is  practically  replaced  by  solu- 
tions of  nicotine  sulfate  which  are  obtaind 
from  refuse  tobacco. 

The  miscible  oils  are  a  standard  remedy  for 
scale  insects  and  are  applied  in  the  winter  or 
spring  before   the   buds   start.     It   is  more 


80  Preparation  of  Substances 

effective  than  the  lime-sulfur  as  it  creeps 
under  the  bark  reaching  all  places.  One 
thoro  application  of  these  oils  will  eliminate 
scale  from  an  orchard. 

When  the  miscible  oil  is  not  properly 
made  by  the  manufacturer  in  the  first  place 
or  when  the  apparatus  used  in  dilution  is  not 
clean  some  free  oil  may  separate  upon  stand- 
ing. If  much  of  any  oil  appears  the  material 
is  worthless  for  spraying  as  the  free  oil  kills 
the  twigs  and  small  lims  by  penetrating  the 
bark. 

In  the  miscible  oils  the  oil  and  the  third 
substance,  a  colloid  in  concentrated  form, 
have  been  put  together  and  it  only  remains 
to  add  water  to  make  the  emulsion.  Their 
condition  is  comparable  to  eg-yolk  which 
consists  of  30  per  cent  fat  diffused  thru  col- 
loidal protein. 

Some  idea  of  emulsions  may  be  gaind  from 
the  following  remarks. 

It  is  possible  to  diffuse  droplets  of  kerosene 
thru  water  by  violent  agitation.  Such  sys- 
tems are  not  stable  as  the  droplets  of  kerosene 
soon  coalesce  and  separate.  This  is  said  to 
be  due  to  the  great  surface  tension  which  is 
a  name  for  the  tendency  of  small  drops  to  get 
together  and  get  the  most  mass  under  the 
least  surface.  Soap  solution  —  a  colloid  — • 
has  a  much  less  surface  tension  than  kero- 


Emulsions  81 

sene  and  droplets  of  kerosene  mixt  with  soap 
solution  will  exist  separately  for  a  long  time. 
There  is  a  second  reason  why  the  kerosene 
will  stay  emulsified.  The  droplet  is  mixt 
with  the  soap  colloid.  The  concentration  of 
the  colloid  is  much  greater  on  the  surface 
of  the  drop  than  elsewhere.  Now  when  the 
droplet  of  kerosene  and  soap  has  reacht  an 
equilibrium,  that  is,  the  concentration  of  the 
soap  solution,  inside,  on  the  surface,  and  out- 
side the  droplets  have  come  into  adjustment, 
a  coahtion  of  two  droplets  of  kerosene  would 
cause  a  readjustment  of  the  concentration 
of  the  solution  on  the  surface  which  would 
require  energy.  Consequently  the  droplet 
once  in  equilibrium  tends  to  be  stable. 


QUESTIONS 
(To  be  answerd  in  the  notebook.) 

5.  What   three   substances   are   necessary   in   an 
emulsion? 

6.  Name  a  colloidal  substance. 

7.  What  is  the  use  of  miscible  oils? 

8.  Which  has  the  greater  surface  tension  soap 
solution  or  water? 

9.  Define  the  term  surface  tension. 

10.  T\Tiere  about  a  droplet  of  liquid  does  a  colloid^ 
when  present,  tend  to  concentrate? 


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